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"Blue's Big Mystery" is the 21st episode of Blue's Clues from the third season.


  • Question: Who is the mystery builder?
  • Clues:
    • 1. Footprints
    • 2. A Curvy Skinny Tail
    • 3. A Picture (Ears)
  • Answer to Blue's Clues: A kitten (Periwinkle)
  • Living room picture: Mrs. Pepper as a detective (first just a silhouette, then a gray silhouette, then a black and grey with dots silhouette)
  • Felt Frame picture: Freddy as a detective


There is somebody building a fort in the backyard of the Blue's Clues house, but they have no idea who it is. So they put on their detective caps to find it out! There is a mystery to be solved. Come along as they investigate, with a little help from Mr. Salt and all of their friends.


Steve invites the viewers inside, saying that something very mysterious happened. Steve reviews what happened in a black and white flashback sequence in which he and Blue were outside playing Kick the Ball when Blue kicked the ball really hard, it flew past a stone wall and he decided to go get it. Once there, he found a cardboard box and a stack of logs, it looks like someone has been building a fort in the backyard, but he has no idea who built it. He did not build it, and Blue didn't, either. He wonders if the viewers built it, but the viewers said that they did not build that fort in the backyard. So it's a mystery, one that they want to solve. Blue leaves her paw-print on the screen saying they should play Blue's Clues. and be detectives and search around for clues to help them figure out the answer to this big mystery. After Steve brushed up on the rules for the game, the paw-print tip-toed and Steve was in shock and asked the viewers where the paw-print went. The viewers saw the paw-print went to the left of the screen and vanished leaving little marks behind on the screen but eventually they disappeared soon after.

Steve goes to Sidetable to get his notebook. Sidetable spoke in a Sherlock Holmes accent and hands Steve his notebook so he can draw out the clues to their big mystery. They follow a tip from Mr. Salt during the mysterious builder hunting season and find a leaf. Using logic and observation, they match it to the proper tree that it came from and choosing a narrowing set of trees. After figuring out what tree the brown maple leaf came from, Steve finds a clue on footprints with four toes. After drawing the first clue, Blue comes in and Steve tells her that he and the viewers found the first clue. The footprints that Steve drew were not Blue's footprints. Steve knew that the clue is like evidence. And because the first clue was footprints, that meant the mystery builder has to have feet. Blue did not know the answer and then Steve decides to follow the footprints and see if he and the viewers can figure out the feet that made them. The footprints stopped by the garden, Pail was watering the garden. Steve hides behind the tree and peeks out and he realized that Pail did not make those footprints. So, they looked somewhere else. Gopher poked his head up from the ground and disappears underneath. Steve and Blue find Tickety who does so have feet. She was doing a jigsaw puzzle and when she was finished, they wanted to talk to Tickety on some evidence. Steve and Blue wanted to be sure that Tickety has feet and she does. So, Tickety was instructed by Steve to make footprints in the dirt. After that, the viewers figured out that Tickety's footprints were a different shape from the ones left by the mystery builder. It did not match the evidence and Steve and Blue thanked Tickety for their cooperation.

Then it was Mailtime. They sing the Mail time song and then Mailbox came inside with a disguise. Mailbox whispers to Steve that he has something for him. It was a mystery letter. Steve gets the mystery letter and when he opened it, there was a leaf inside which looked just like the one he saw and found before. Shovel calls Steve to take a look at the fort outside. Steve did so and Pail tells Steve the fort was growing. There was a roof put on top of the cardboard fort which had leaves that looked a lot like what Steve has in his hand. Steve thought the mystery builder has struck again. Soon after, a paw-print appears behind the bushes. It disappears, then it reappears and gets away. Steve did not see it and asked the viewers where the clue went. The viewers call out "left" and Steve said "follow that clue!" Now, they find signs of activity at the house next door to the Blue's Clues house. Could somebody be moving in? Steve thought the second clue had to be by the house next door. The clue appears and disappears and different spots and Steve was just not quick enough to see it. Steve still had to draw the second clue but did not know what the second clue was. The viewers remembered that it was a tail. Steve gets the notebook out and was about to draw the clue when he realized that he did not see the tail. How can he draw something he did not see? Steve asks the viewers if it was a straight tail or a curvy tail. The viewers saw a curvy tail. Steve needed a little more info and asks if it was bushy or skinny. The viewers saw that it was a skinny tail. Now that Steve had enough info, he carefully draws a curvy, skinny tail. He shows the viewers the second clue. Steve was struggling to figure out who the mystery builder could be.

The first clue was footprints and the second clue was a curvy, skinny tail. Steve needed one more clue to solve this mystery. Mr. Salt calls out from afar and thinks he saw the mystery builder. Steve and Blue looked at three photos taken by Mr. Salt himself. Mr. Salt missed three times but had to be some evidence in one of the three pictures of where the mystery builder went. The viewers pointed out some evidence taken by the stone wall because they noticed the tail sticking out. Steve saw the viewers were right and was amazed and their detective work. Steve and Blue looked by the stone wall but when they got there, the tail was gone. The viewers saw footprints on the path which started next to the stone wall. The footprints on the path were the ones Steve drew earlier in his notebook and it was their main evidence. Steve and Blue followed the footprints but then they stopped. The footprints go in two different directions. Steve and Blue checked the set of footprints on the path going straight to the left. Then, they heard something. Gopher pops up by the leaf pile. Steve and Blue thought Gopher was the mystery builder. Gopher had footprints that matched the ones Steve drew in his notebook but Gopher's tail was skinny but it was not curvy and it was very short and stubby too. Steve and Blue now know that Gopher was not the mystery builder. As Gopher left, Steve and the viewers that they solved it and now they had to check the set of footprints going downwards. Then, the footprints ended by the sandbox. Steve and Blue were stumped. Steve asks the viewers where the mystery builder went this time. The viewers pointed out the tire swing which was still swinging and thought somebody must have just pushed it. Steve and Blue pass the tire swing and up by the fort again. Steve and Blue looked around for the mystery builder and knows that it has be around here someplace. Mr. Salt takes a picture and when the picture came out of the camera, the third clue was on it. Mr. Salt felt bad because he got a little too close. Steve understood and it was okay because Steve can still draw out the clue in the notebook. The third clue had a point, a curve, and another point. Now that Steve has collected all three clues, they were ready to figure out the mystery. Steve thought Mr. Salt did a great job for his hard work. Steve sits in the thinking chair and he and the viewers had to think who the mystery builder was that built the fort and was moving in next door to their house. The clues were footprints, a curvy, skinny tail, and a picture with two points and a curve in the middle. Steve looks at the third clue and can see two triangles. He asks the viewers what the two triangles with the curve in the middle is called on top. The viewers saw that they were ears. Steve thought those ears on top would have to be the picture of the mystery builder's head. Steve had to figure out who had a head with pointy ears, a curvy, skinny tail, and made footprints that Steve and Blue were following on the paths. All those clues turned out to be a kitten because a kitten had a curvy, skinny tail with pointy ears on its head and made footprints next to the stone wall and what Steve and Blue were following.

Now that they know what they are looking for, they head outside once more and find the kitten. It takes Steve and Blue a minute to find him, but once they do, Steve asks him for his name. He asks for their names and they tell him and he introduces himself as Periwinkle. It turns out he has moved in next door and has been building his fort outside, not knowing anything about his new neighbors. Mr. Salt takes a picture of him and Blue. Mr. Salt welcomes Periwinkle into their neighborhood and gives the picture of himself with Blue. After that, Steve sings the "So Long Song" and the episode ends outside with Periwinkle and Blue in the cardboard fort.

Video Releases




Watch Episode

This episode is available for streaming on Paramount Global's video streaming service Paramount+.


  • Nick Regina is one of Steve's Friends in this episode. He's related to Jessie Regina, a friend of Steve from Blue's Big Musical.
  • This episode acts like a mystery episode.
  • In the US version, we clearly hear Steve narrate the prior events via flashback, same goes with Kevin in the UK version, but in the Portugal version, there is no narration.
  • This is the first episode to have Mailbox and Periwinkle appear during the closing credits. Periwinkle would later appear more often during that, starting with Season 5.
  • This is the second time Steve gives out the wrong answer during the first clue.
  • When Steve asks Sidetable for the Notebook, she spoke in a Sherlock Holmes accent to him as she closes her eyes halfway through.
  • When Steve opens a letter, he doesn't get the Video Letter segment, because the Video Letter replaces with a leaf.
  • After Steve and Blue figure out the answer to Blue's Clues, a picture of Mrs. Pepper is seen on the picture frame to the right of the thinking chair.
  • This is the first episode with no skidoo segment.
    • This is one of the two episodes in Season 3 to not have a Skidoo segment, the other is Magenta Gets Glasses.
  • This episode takes place in fall, as the color of trees' leaves are yellow, orange, and red.
  • Every time Steve turns around to try and find the second clue on a tail, it kept disappearing.
    • The same concept happened when Jup Jup didn't want to get found on the Australian TV show, "Hi-5".
  • In this episode, Steve has to draw a clue without him even seeing it.
    • However, the viewer did see the clue.
  • When Playtime with Periwinkle was released as two bonus episodes on the 2004 DVD release of Blue Talks, the TV version of this and Periwinkle Misses His Friend were used.
  • In this episode, Steve gets a letter but instead of a video, there is a leaf on there.
  • Several things happened on this episode of Blue's Clues that has never happened before.
    • First of all, Blue did not know the answer to Blue's Clues anymore than Steve or us do.
    • Second of all, the clues appeared without Blue ever placing her pawprint on them.
    • Thirdly, there was no Skidoo segment.
  • Pieces of the mystery music used in this episode was from "What Does Blue Want to Do with Her Picture?".
  • This episode is the first of two on "Playtime with Periwinkle" VHS.
  • The "No" voiceover is used from "What Was Blue's Dream About?".
  • Catharine Mullally, Maggie McGuire, and Beth Mayerowitz all receive Special Thanks credits.
  • In the credits, Todd Kessler as an executive producer is credited at the end instead of close to the beginning for the first time.
    • This was put to permanent use starting with Inventions, and the last episode to use this was Café Blue.
  • This is the second episode Steve doesn't get a video letter, he instead just gets a normal letter with a big maple leaf in it, the first episode was Blue's Big Treasure Hunt.
  • This episode introduces the character of Periwinkle, as voiced by Cameron Bowen. At first, he is credited as one of "Steve's Friends" in the past but is soon added to the list of cast credited along with the name of their character. At the start of the fourth season, he is replaced by Kenny Kim as the voice of Periwinkle.
  • How Blue got a paw print on the tail and the picture as the 2nd and third clue is unclear and doesn't make sense, since Blue could've been seen by Periwinkle when she placed her pawprint on his tail and the 3rd clue was seen on the picture after it came out of the camera's exit slot. It may have been possible that Blue saw the tail and carefully placed her paw print on the tail and left before she was noticed, and placed a paw print on the interior of the fort in the exact position where Mr. Salt took the picture.
  • Just like What Is Blue Afraid Of?, this episode is considered spooky.
  • This is the second episode where No! is heard from What Was Blue's Dream About?.
  • This is the sixth episode where two clues are found and drawn outside with only one clue found inside.
  • This is the first episode during the intro, the door of the house appears more purple.
  • This is one of the only times where Steve finds the clue just as fast as the viewer does (which was the third clue). The first time this happened was in What Does Blue Want to Do on a Rainy Day?, when he and the viewers both found a clue on a marching toy at the exact same time and he does it again in Blue's Big Musical, where he found a clue before the viewers did. However, unlike the two, Steve doesn't tell the viewers that he found a clue just like them.
  • When Steve was thinking about the first clue, his hair from the next aired episode was used.
  • Some of the voiceovers from this episode would be used in later episodes. As an example, The Wrong Shirt has some of them.
  • In the credits, Shovel appears by himself and without Pail for the first time. Mailbox also appears for the first time in a credit sequence. And so does Periwinkle, but he does a one-time action by sneaking around. His permanent action will debut in Blue's Predictions. The shot of the Blue's Clues book does not fade away, rather cutting instead. This also happens in Blue's Play, Prehistoric Blue, Superfriends, and Bugs!.
  • Mr. Salt appears without Mrs. Pepper, except during the credits.
Blue's Clues Season 3
Blue's Big Treasure Hunt | Art Appreciation | Weight and Balance | What's That Sound? | Animal Behavior! | Blue's Big Pajama Party | Draw Along with Blue | Hide and Seek | Thankful | Blue's Big Holiday | Pool Party | Anatomy | Signs | Nature | Geography | Occupations | Blue's Big Mystery | Periwinkle Misses His Friend | Blue's Big Musical | What's So Funny? | Blue's Big Costume Party | Inventions | Blue's Play | Prehistoric Blue | The Wrong Shirt | Words | Shy | Magenta Gets Glasses | Environments | Stormy Weather | Blue's Collection | Café Blue