Didi and Grandpa Lou visit an antique store / frozen yogurt shop called "Cold N' Oldies" and discover a strange mirror, which the Rugrats use to go to "Mirrorland", the place where "everything is the same, only different".
- - Description from Klasky Csupo.
While the babies explore the fish tank and Grandpa Lou is sleep in front of the tv, Didi brings home an antique mirror. Of course being the curious babies they are Tommy, Chuckie, Phil, and Lil go up to it wondering what it is, and what it does.Tommy walks over to the mirror curious as he sees his reflection being mesmerized by it as he begins playing with it.
Meanwhile Lou helps Didi bring in the other stuff she brought while she was out. The babies are playing with their reflections in the mirror, of course Phil and Lil being twins they're each others mirror. They all then wonder how a mirror works as Chuckie tells them they probably wouldn't understand but ends up telling how when they look into the mirror that they're actually seeing a person like them and a whole other world on the other side, aka Mirrorland as Tommy refers it to. Chuckie keeps explaining as he says everything in Mirrorland is backwards. Tommy, Phil, and Lil find it pretty silly but accept it since it's Mirrorland , and of course want to go to Mirrorland. Chuckie of course tries to stop them as he tells them that they couldn't go because there's always a Mirror boy in the way.
Tommy then moves back and runs towards the mirror only for Didi to grab him before he hit the mirror and hurt himself. Which this cause Lou to drop the box he and Didi were carrying inside. Didi of course put the babies in the playpen telling Tommy to play with soft things. Didi then carries the mirror upstairs while Lou discovers what's in the box. Chuckie then says to Tommy that run into the mirror probably wasn't a good idea in which Tommy actually agrees then saying that they needed to outsmart the mirror boys.
Didi is decorating the house with the things she brought as she puts up a cat clock, trying to get it to work only for it to work for a few seconds before it stops again. Lou then brings in the box as he shows Didi the things inside as Didi tells him it's only junk when Lou puts on an old toupee. Of course a ballerina outfit catches her eye and she decides to go and try it on. While Didi and Lou are doing that Tommy and Chuckie escape the playpen in search for the mirror as Chuckie tries to talk Tommy out of it saying something bad will happen of course Tommy ignores as usual as he tells Phil and Lil once he and Chuckie come back they'd get a turn.
Tommy and Chuckie then go off in search of the mirror while Didi is trying on the outfit. Didi's glasses fall off her face onto the floor in which Spike takes them and heads down stairs just as Tommy and Chuckie get up the stairs. They then spot the mirror in a nearby room, Meanwhile Lou is trying on the toupees that he found in the box as Didi says she can't find her glasses and askes Lou if he could help her find him. Back to Tommy and Chuckie, Tommy walks closer to the mirror as he tells Chuckie his plan as he is going to use his favorite ball knowing that it was possibly the mirror boys favorite ball. Tommy then had Chuckie call out to the mirror boy so he would look at it, given them a chance to enter Mirrorland.
Tommy, when he gets the chance, goes and runs into the mirror causing it to flip lifting up Tommy and throwing him into a box behind it. Chuckie then walks up and the same thing happens to him as he lands into the box as well. After climbing out of the box Tommy and Chuckie think they actually went through the mirror and were now in Mirrorland. Meanwhile Phil and Lil fight about who's right, that if Chuckie and Tommy made it to Mirrorland or not, as Spike, still holding Didi's glasses in his mouth then goes into the kitchen and knocks the box full of toupees onto the floor getting him all dusty and dirty. Tommy and Chuckie explore the upstairs wondering what else was different, of course everything look the same, but Tommy claimed it was different as he tells Chuckie many different things like wearing shoes on your hands, sleeping under the bed, and wearing your diaper on your head, as Tommy takes off his diaper and puts it on his head.
Chuckie then wonders if there really is a Mirrorland and not just something Tommy is making up. Tommy and Chuckie then hear Grandpa Lou as Tommy quickly puts his diaper back on as he and Chuckie hide. Lou then comes in the room looking for Didi's glasses wearing a giant red toupee causing the babies to think it was Mirror Grandpa and that he was mean. Tommy and Chuckie then run out the room only to see Didi walking blindly down the hall wearing the Ballerina outfit thinking she is the mirror version of Tommy's mom and think she's a robot as she walks and trips in a closet. Tommy and Chuckie then run back to the room that had the mirror only to run into "Mirror Spike" as they run and hide in the guest bedroom as Tommy tells Chuckie to hand him his ball as he throws it in which Spike of course chases after it.
Tommy and Chuckie then head for the mirror while spike runs downstairs chasing the ball only to run into Lou who takes Didi's glasses off of Spikes face and gives them back to Didi. Didi is surprised by the toupee and tells Lou to take it off as she goes upstairs to change out of the Ballerina outfit as the skirt was a bit short. Lou then took Spike to give him a bath while Phil and Lil still argued if Tommy and Chuckie got to Mirrorland or not. Tommy and Chuckie get back to the mirror and without another thought run towards it causing it to flip around and flip them back to the front making it seem like they went back through the mirror.
Didi then comes in, dressed in her normal attire, as she takes Tommy and Chuckie back down to the playpen. Didi then overhears Lou having trouble washing off Spike and goes to see while Phil and Lil ask Tommy and Chuckie questions about Mirrorland. Phil and Lil then suspect Tommy and Chuckie are mirror boys and makes them answer questions in which only the real Tommy and Chuckie would know. Chuckie of course hesitated when answering causing Phil and Lil to call him a mirror boy but he finally answers as they all burst out laughing. Spike, still wet, then jumps into the playpen and licks Tommy as the twins say that Tommy and Chuckie couldn't be mirror boys since dogs could tell. In the end Didi says the babies can be a handful sometimes but are adorable as Lou says he's going to wash up.
- This episode is used as a basis for a mini-game in the PlayStation game Rugrats: Search for Reptar.
- The room the mirror is in, in the episode is a guest room in the mini game of Rugrats: Search for Reptar.
- We get to see the adults play dress up in this episode. Look for spike trying on a false beard and glasses, Didi in a ballerina outfit, and Grandpa Lou trying on rock star wigs.
- When Lil says she's glad the boys are back, you can hear Kath Soucie's voice slip into Phil's voice at the end.
- Didi's mouth doesn't move Uh-Oh.
- when tommy and Chuckie first go into Tommy’s parents room the bed has no shoes but appear in the shot after.
- in the end there’s a shot of Phil and lil with their ducks missing from their outfits.