The VHS of the movie was released in September 1999, a few months after production on Doug ceased. It contained a bonus feature at the end, known as a "Doug-Umentary", which features the creator answering the top ten questions kids ask about Doug. After thirteen years, the film was finally released on DVD in 2012, though it is only available to members of the Disney Movie Club and did not include any special features.
The movie opens when Doug and Skeeter are at Lucky Duck Lake being harassed by Roger and his friends.
Doug and Skeeter discover a monster that lives in Lucky Duck Lake. At first they are scared of him, but they later on find him to be nice. But the monster is proof that Bill Bluff is polluting the lake, which is what created this monster to begin with. The Monster almost eats the book Moby Dick, but Skeeter stops him and says, "Stop! You almost ate Herman Melville", and the monster responds, so they name him Herman Melville. They show it to Mrs. Dink, who's the mayor. She tells Doug and Skeeter not to tell anyone about Herman and the polluted lake or else Mr. Bluff will kill the story. Mrs. Dink tries to come up with a plan to make sure Mr. Bluff would not interfere. But all this commotion with the monster makes Doug forget that he was supposed to meet Patti at Mr. Swirly's. When he remembers this, he runs to Swirly's as fast as he can using the quickest shortcuts that he knows. Once he gets there, he doesn't see Patti. He asks Mr. Swirly if he's seen her, and he says the she was here for a while and looked very upset, and then left with a guy who kept talking about his big plans for a dance. When Doug hears this, he knew that this guy was no one else but Guy Graham, a snobby upper classman who wants Patti. Meanwhile, Roger and the AV nerds are building a robot to kidnap Herman, but when they build the robot it, acts like Roger's babysitter.
Doug then rushes to the Funkytown night club, where Guy and Patti are working on the dance. He apologizes to Patti there and she accepts his apology. But Guy cuts in and says that Doug is just a stupid little kid. Doug, very angry now, says that he has proof that Bluff is polluting the lake (Doug goes against Mrs. Dink's warning). Guy then calls Doug a liar. Doug then invites them both to the report that is being held in front of Mr. Dink's house about Herman and the pollution. Doug then leaves, but the picture of the monster falls out of his pocket without him knowing. Guy picks up the picture and realizes that Doug was telling the truth; he then calls Bluff, with whom he has connections to. The next day, Patti asked Doug to bring Guy. Doug allows it in hopes to get back at him. At the reporting, Doug sees that a news reporters camera is inflatable. He then realizes that the news company is a fake, that it is supporting Bill Bluff and trying to compensate the monster. Doug then has to tell everyone that there has been a mistake, Patti gets mad at him, thinks that he is a liar and walks away with Guy.
That night, Bluff finds the boys with Herman and kidnaps the monster. The next morning, Doug knows that this is his last chance to save Herman. He goes to the school newspaper room, hoping to find Guy, who can lead him to Bluff. Hoping he can asked Guy for help and he was going to swallow his pride for nothing because Guy wasn't going to help him. Guy isn't in the room, but Doug sees a newspaper article that says that Bluff and his men have blasted the monster to smitherines at the school dance. Doug is at first sad and believes that Herman has died, but he then realizes that the school dance isn't until tonight and this is what is being planned to happen. Doug and Skeeter call Roger and The Sleech twins to help. At the school dance, he has to make the biggest choice of his life, going after Patti or saving Herman. When he does that, Bluff catches the quintet in front of Crystal Lake and starts to enslave them, but is stopped by Mrs. Dink. Beebe arrives and forces her father off of the scene to defend her friends. Doug then finds Patti in front of the woods and Doug tries to tell her he is in love with her but is interrupted by Herman. With the return of Herman and a copy of the newspaper, Patti sees that Doug had been telling her the truth all along and dumps Guy. Also, Skeeter gives Herman the Moby Dick book for something to eat in the lake and Herman also gives Doug a flower to give to Porkchop to which Porkchop comes running out of the woods into Herman's arms. Doug, Skeeter, Patti, Porkchop, Roger, The Twins, and Bebe say goodbye to Herman; after Herman jumps back into the lake, Doug tells Patti he likes her and Roger almost becomes friends with Doug, but is interrupted by the robot. Doug starts dancing with Patti and Skeeter dances with Beebe.
- Thomas McHugh as Doug Funnie
- Fred Newman as Skeeter Valentine/Mr. Dink/Porkchop/Stinky
- Chris Phillips as Roger Klotz/Boomer/Larry/Mr. Chimminy
- Constance Shulman as Patti Mayonnaise
- Alice Playten as Beebe Bluff
- Doug Preis as Bill Bluff/Phil Funnie/Willy/Chalky/Agent 1
- Guy Hadely as Guy Graham