Scooby-Doo! Curse of the Lake Monster is a TV movie which combines live-action with computer generated animation. The film first aired in the United States on the Cartoon Network on October 16, 2010 and was released on DVD on March 1, 2011. It is based on characters which first appeared in a Hanna-Barbera cartoon series in 1969. The film is the fourth live-action Scooby-Doo movie and a direct sequel to the 2009 TV movie Scooby Doo! The Mystery Begins.
In common with most stories from the Scooby-Doo franchise, the film centers around the characters of the four teenagers Fred, Daphne, Shaggy and Velma and Shaggy's pet dog, a Great Dane named Scooby-Doo, and follows them as they attempt to solve a seemingly supernatural mystery. In Scooby-Doo! Curse of the Lake Monster, the four teenagers get summer jobs at Daphne's rich uncle's country club in a lakeside town. Their jobs are put in jeopardy when a monster appears at the country club and frightens most of its members away. In order to help Daphne's uncle and to save their jobs, the four young people determine to find out the truth about the monster. Sub-plots deal with Shaggy falling in love with Velma and overcoming his shyness to reveal his true feelings to her and with a short lived romantic relationship between Daphne and Fred.
The film stars Nick Palatas as Shaggy, Hayley Kiyoko as Velma, Kate Melton as Daphne, Robbie Amell as Fred and Frank Welker as the voice of Scooby-Doo. It was rated PG by the Motion Picture Association of America for some mildly scary moments.
In the town of Coolsville, the high school has just closed for the summer. The four students Daphne, Fred, Shaggy and Velma and the dog Scooby-Doo leave for the town of Erie Pointe on Lake Erie, where the four teenagers are to take up summer jobs at a country club which belongs to Daphne's wealthy uncle. Daphne and Fred have recently become boyfriend and girlfriend but, due to their different attitudes towards relationships and their jealousies of each other, their relationship does not last very long.
When they stop to ask directions at a store called Trowburg's Gas and Goods, an old woman warns the teenagers not to go to the country club and to leave while they still can, telling them that the monster in the lake is likely to return and terrorize the town again. Shaggy is terrified by what the woman says but the others dismiss it as a typical small town legend which is used to attract tourists.
On arrival at the country club, Shaggy suddenly falls in love with Velma. After work, he accompanies Velma when she takes a walk on the beach. Velma finds a gem in the sand, which she identifies as a moonstone, and then suddenly begins to feel sick and want to go back to her room.
The four teenagers and their dog are invited to a party at the country club that evening, Velma is unable to attend because she is still feeling ill. The party comes to an abrupt end when the monster appears. The creature is the size of a man but it resembles a frog with a mouth full of sharp fangs. All of the guests flee in terror and most of them cancel their country club membership, leading Daphne's uncle to contemplate closing the club. The teenagers decide to find out the truth about the lake monster, deciding to start by visiting the only person ever to have claimed to have photographed the monster, Mr. Uggins the lighthouse keeper.
On the beach near the lighthouse, the gang appear to encounter the lake monster again, although it turns out just to be Mr. Uggins in a costume and a mask. He reveals that he never really saw the creature and he simply photographed himself in the costume as a way of making some money. He insists that he was not the one who was at the country club earlier, says that the lake monster is real and goes on to tell the legend behind it. When settlers first arrived at Erie Pointe, they found that an old woman named Wanda Grubwort was already living in the caves by the lake. She told them that all the land around the lake belonged to her and told them to leave. When the settlers ignored her, Wanda Grubwort used magic to trnasform a frog into the lake monster and commanded it to do her bidding. Wanda Grubwort was later found guilty of witchcraft and put to death, although her evil deeds seem to live on.
The following day, Velma shows the others that footage from the country club's security cameras show the lake monster talking to someone in a hooded robe. Velma spills tea on the computer, destroying the footage, before she can zoom in on the person's face.
That evening, Daphne, Fred, Shaggy and Scooby encounter and escape from the lake monster again. While hiding from it, Shaggy finds another moonstone which he decides to give to Velma later. When Shaggy points out that Velma is missing, the others go looking for her. They find her the following morning, lying unconscious on the beach. When she comes round, she claims not to remember much about the night before. The others also notice that she has warts on her hand.
Shaggy having finally gotten up the courage to ask Velma out on a date, the two go to a restaurant that evening. Scooby, jealous of the attention that Shaggy is giving Velma instead of him, attempts to sabotage the date and it comes to an abrupt end when Shaggy gives Velma the moonstone, the girl rushing off as soon as she gets it.
Meanwhile, Daphne having remembered that the figure which they saw had purple paint on its robe, Daphne and Fred decide to investigate a purple and pink boat which they saw when they arrived in town. The boat turns out to be a floating museum, on which Daphne and Fred find several old newspapers with stories about Wanda Grubwort. They learn that, after Wanda Grubwort's death, her magical staff was broken into pieces which were scattered around the town. They also learn that her children were later found living in the cave, meaning that she may still have living descendants in the town. While they are looking at the newspaers, the lake monster comes onto the boat, locks the door of the room which Daphne and Fred are in, turns up the water pressure, causing the pipes to burst and flood the room in. Daphne and Fred just manage to escape in time.
The gang search the local phone book for anybody named Grubwort but are unable to find one. Noticing the reflection in the mirror of an advertisement for Trowburg's Gas and Goods on the back of the phone book, Shaggy points out that Trowburg is Grubwort backwards. Daphne, Fred and Shaggy go to the home of the woman who runs the store. They find the mysterious robed figure inside but, when they remove her hood, they are surprised to find that it is Velma. The moonstone which she found came from Wanda Grubwort's magical staff, the witch began to take her over when she found it. She put the witch's staff back together, began to physically transform into Wanda Grubwort, hence the warts, and was the one in control of the lake monster.
When Velma flees, the owner of the house tells the others that she will have gone to Wanda Grubwort's old home in the caves by the lake. The others follow her there, where she transforms more frogs into lake monsters which chase Daphne and Fred. Shaggy tries to talk to Velma, telling her to fight the spirit of the old witch who is trying to take over her body. He tells Velma how much he likes her and gets her to join in singing her favorite song. She drops Wonda Grubwort's magical staff, which Scooby snatches and destroys. The source of Wanda Grubwort's magic having gone, the lake monsters that were chasing Daphne and Fred change back to harmless frogs. Wanda Grubwort's ghost briefly appears, complaing that the "meddling kids and that darned dog" ruined her plans, before vanishing.
Shaggy kisses Velma, but the two realize that there is no chemistry between them. Daphne and Fred also decide that their relationship was not meant to be and the four of them are better off just being friends.
As a reward for saving his country club, Daphne's uncle gives the teenagers $10,000. They decide to use the money to found Mystery Inc. and to continue using their talents to solve mysteries.