Inspector Austin of the Paris police is chasing down Le Master of Disguise, who he can only identify with his nasty laugh. Can he find Le Master of Disguise from the passengers of the train, including the Conductor, a Cowboy, and Tasha the Circus Balancer, before the train reaches Istanbul and Le Master of Disguise makes his escape?
Pablo is in the backyard wearing a black hat. He introduces himself to the viewer as Le Master of Disguise, a wanted trickster who is trying to escape to Istanbul where he is safe. He sings Le Master Of Disguiseas he swaps outifts to prove how he is the best at disguising and tricking others. He then hears Austin of the Paris Police looking for him and runs off. Austin steps on screen, looking for the wanted criminal.
Austin questions the viewer about Le Master of Disguise's current residence as the backyard transforms into a train station. A conductor (that looks surprisingly similar to Pablo) shouts "All aboard!" multiple times. Austin confronts the so-called conductor and asks him if he has seen Le Master of Disguise. The conductor replies with a no and causes a disappointed Austin.
Austin searches for the criminal as two passengers enter the train, a cowboy and a circus performer. Austin tells himself that anyone of the train's passengers could truly be the criminal until he hears Le Master of Disguise's famous laugh, being performed by the conductor. The train heads for Istanbul. Austin jumps on at the last minute and finds another conductor, Uniqua. Austin predicts that the new conductor is obviously Le Master of Disguise.
Uniqua tells Austin that she has no idea what he is talking about since she truly is the train's only conductor. Austin then faces the truth: the previous conductor was the criminal and tricked him. The two sing Who Can It Be? as they search for Le Master of Disguise. They come across a beanery (a restaurant located inside the train).
Austin spots the cowboy he saw earlier, suspecting him to be Le Master of Disguise. The duo questions the western moose to prove that he is a real cowboy. Tyrone the cowboy tells the two that he could do some rope tricks for them and does so, while singing I'm a Cowboy. Austin jumps to the true conclusion of the mystery: Tyrone really is a cowboy, not Le Master of Disguise.
The waiter at the beanery laughs Le Master of Disguise's famous laugh, proving that he is Le Master of Disguise. Austin and Uniqua turn around, expecting to catch the criminal, but Pablo escapes into the storage area. Uniqua and Austin follow him, only to find the circus performer Austin spotted earlier.
Austin tells Tasha the circus balancer to prove that she truly is a circus actor. Tasha balances on a tightrope while singing Could Le Master of Disguise Do This? to prove that she is not Le Master of Disguise. Austin accepts the proof as he hears the laugh once again. Austin opens the door on the last cart and looks for Pablo after telling Uniqua to round up the passengers to make sure none of them is Le Master of Disguise.
Austin knows that, since he is on the last car and the train is going to fast for someone to jump off of without getting painfully injured, that Pablo must be on top of the train. Austin finds Pablo running away from him on top of the train cars. Austin loses track of Pablo and reports his information to Uniqua.
Tyrone, Tasha, and Uniqua enter the beanery and wait for Austin. A disguised Pablo made to look like Austin enters the room as Austin does as well. The two fight over who is real Inspector. Austin forgets what he is supposed to do after he caught Pablo since he never thought he would make it this far.
Pablo asks why Austin was chasing him in the first place. Austin claims to not know as Pablo invites everyone over for croissants at his house. The train transforms back into the backyard as the children sing the end song. They enter Pablo's blue-colored house. Pablo opens the previously closed door and shouts "Heh-heh-heh!", his famous laugh.