Scooby-Doo! Curse of the Lake Monster (also known as Scooby-Doo 4 or Scooby-Doo 4: Curse of the Lake Monster) is a live action/CGI television film by Warner Premiere for Cartoon Network, based on the Saturday-morning cartoon series Scooby-Doo by Hanna-Barbera. It is the fourth live-action Scooby-Doo film. Director Brian Levant, producer Brian Gilbert and writers Daniel Altiere and Steven Altiere regroup for this production. Scooby-Doo appears as a computer-generated animation produced by the Animation Picture Company. The Atlas Entertainment production also contains the previous live-action cast from Scooby-Doo! The Mystery Begins. The film premiered on October 16, 2010.
School has just ended. Velma (Hayley Kiyoko) and Shaggy (Nick Palatas) are waiting by the van for Fred (Robbie Amell) and Daphne (Kate Melton) so they can go to meet Daphne's Uncle, who has given them summer jobs at his country club in Erie Point so the gang can pay for the damage they did to a barn setting it on fire during one of their mysteries. They then find Fred and Daphne making out in the back of the van. Daphne reveals that they started dating after she fell out of the top of the barn from the mystery that enabled them to get the summer jobs and he had caught her, making her realize that he was "the one." Velma warns them that often when two people in a group start dating, any changes of that relationship affects the whole group, but the two don't seem to care.
On the way to the country club, Fred gets lost. They stop at a small country store called Trowburg's, where a seemingly crazy woman tells them that she warned them not to build the country club, and that the Lake Monster will return. Velma tells them that there have been sightings of the lake monster for hundreds of years. Shaggy immediately rejects the idea of going any farther, but the rest of the gang ignores him. When they arrive there, they are greeted by Daphne's Uncle, Thornton "Thorny" Blake V. He shows them to their quarters, and when Shaggy is getting his bags off the top of the Mystery Machine, he falls off and is caught by Velma, with whom he then falls in love. Shaggy asks Scooby (Frank Welker) whether there is any chance of him and Velma.
The next day, Shaggy is caddying with Fred, when he asks Fred for dating advice. Fred tells him that Daphne wasn't his girlfriend; they were just 'hanging out'. He says that he doesn't think their too serious and that he like "playing the field". Meanwhile, Daphne is telling Velma about her relationship with Fred, and saying the exact opposite - that Fred's totally her boyfriend, and he doesn't like playing the field, and things were getting serious. They meet at the pool, where Daphne tells them that they're all invited to attend the opening party for the country club. While she and Fred take a swim, Shaggy takes a walk on the beach with Velma.
He is struggling to say he likes her, but she isn't paying any attention. Velma is talking about the underwater caves when she finds a moonstone. She says she loves them, and Shaggy begins to tell her that her eyes are beautiful, when Velma suddenly gets nauseous. Shaggy tells her she needs to sit down and asks her if she's all right, but she just says she'll return to her cabin and lie down. Shaggy seems a bit shocked.
That night at the party, a huge frog-like monster suddenly appears and wreaks havoc on everyone. After everyone leaves, Uncle Thorny tells the gang that almost half of members quit, and if someone doesn't do something, he might have to close down the club. The gang decides to help him solve the mystery. They decide to investigate the only person who has ever taken a picture of the lake monster, Mr. Uggins. He is also the lighthouse keeper. Shaggy suggests splitting and insists on going with Velma. They're walking on the beach, and she quotes an old song about the moon, which is says she loves. Shaggy is then sucked into a daydream when he is singing to Velma. However, he is interrupted when they see the lake monster.
Meanwhile, Daphne is talking to Fred about how she thinks Shaggy likes Velma, when Fred says that Shaggy must have not followed his advice. Daphne begins to ask him what he means when they hear the screaming of Shaggy and Velma. The lake monster falls, and turns out to be Mr. Uggins, who said that he decided to take that picture to make a quick buck, but it wasn't him last night at the party. He then tells them the story of the lake monster: how when people were first settling Erie Point, an old woman named Wanda Grubwort warned them not to come onto her land. They paid no attention to her, so she used her magic staff - which used moonstones as the source of her power - to turn a frog into a horrible monster that attacked the villagers. Wanda was later tried for witchery and burnt at the stake. The next day, Daphne finds Shaggy writing "Mr. Shaggy Dinkley" and "Mrs. Velma Rogers" all over the napkins outside. He eats the napkin, saying that his doctor told him he needs more linen in his diet, and tells her that Fred is off putting with some girls.
Daphne sees him hugging them and becomes jealous and angry, and when Fred comes up is very irritated with him, though she doesn't explain why. Shaggy then begins to ask them about dating advice for his friend "Scruffy", but then Velma appears, with important evidence. She shows them the security footage of the lake monster's attack last night, and it shows the lake monster meeting a mysteriously masked figure on the beach. They begin to zoom in on the figure to see its face, but Velma accidentally spills her green tea on the computer and destroys the footage. Depressed and ashamed, she walks away, though Shaggy tries to convince her to stay. He then admits that he likes her to Fred and Daphne. They start to give him advice, but they end up arguing about their relationship, and Shaggy lets it slip that Fred told him they had a "loosey-goosey" relationship. Daphne angrily storms away. Shaggy is pretending that Scooby-Doo is Velma later that night. Scooby impatiently tries to do something familiar with Shaggy, by making a monstrous midnight snack, but Shaggy smells Velma's scent and drifts away to find her, leaving Scooby steaming mad. Meanwhile, Fred is out jogging when he sees Daphne playing tennis with a couple of boys - a plot to make Fred jealous. Fred is obviously annoyed, but before he can say anything, they hear Shaggy screaming. They run to find him and they also find the lake monster. Fred and Daphne run one way while Shaggy runs the other. He's cornered by the lake monster, but Scooby Doo rides over on a four-wheeler and saves him.
He then crashes into a sand pit where Shaggy finds a moonstone, saying that Velma loves them. Fred and Daphne are hiding by the golf carts - with Fred still trying to find out who those tennis players were while still seeming unjealous - when the lake monster appears. Fred tries to fight it, but they end up running for their lives and crashing into Shaggy, who has become terrified that Velma has been eaten. The next morning, they find her unconscious on the beach. Daphne and Shaggy both thinks she's dead and starts crying, but Velma then wakes up. She says she was out walking when the fog rolled in. Shaggy begins to tell her that he was very worried, but stops when he notices warts on her hand. Velma looks surprised, but guiltily assures them that it's nothing. After they fill her in on the latest monster attack, Daphne says that she saw purple paint on the figure's cloak, and suggests they check out a boat that they saw on the way to Erie Point - one that Shaggy called the "S.S. Daphne" because of its color.
Shaggy doesn't agree and asks Velma out on a date, which she tolerantly says yes to. While Shaggy and Velma are on their date, Fred and Daphne go to see the boat. It is becoming more and more apparent that Fred didn't like Daphne playing with the boys - which Daphne seems to enjoy. On the boat they discover many old newspapers in a closet and learn that the moonstones in Wanda Grubwort's staff were scattered and buried many years ago, and that she had some children which were found in the caves that she lived in. They deduce that Wanda has descendants living in town, and they could be trying to get revenge for what the people did to her. The lake monster then appears and locks them in and turns the water pressure up, bursting the pipes and beginning to flood the closet. While Fred and Daphne desperately try to find a way out, they fight about their relationship problems and break up. Fred finally manages to save them when the water is up to their necks by breaking the closet window with part of the pipe, but Daphne is still furious at him and stomps away. Meanwhile, at Shaggy's date, things go well until he lights a match to light some candles. Velma flings herself back in terror, though she is unsure why. Shaggy calls out the waiter, who turns out to be Scooby Doo, who is angry at Shaggy for ignoring him lately and is trying to ruin the date. Scooby refuses to leave when Shaggy tries to bribe him and instead bites Shaggy, causing Shaggy to knock over the table and drop the moonstone on the ground that he was going to give to Velma as a surprise. When Velma sees the moonstone, she takes it and leaves mysteriously.
When Fred and Daphne, soaking wet, get back to Shaggy's quarters, they find Scooby painting a line between his side of the room and Shaggy's side. Things are still very tense between them, but they share what they found out with Shaggy. They can't find Grubwort in the phone book until Shaggy points out that the name of the country store they visited, Trowburg's, is Grubwort spelled backwards. They drive to the home of the woman who owns Grubwort's. They see the witch's figure through the windows, but they don't split up, due to the strained relationship between Shaggy and Scooby and between Fred and Daphne. The cloaked figure is seen to be a very warty Velma. However, she claims to not be Velma and attacks the gang, knocking them out for a moment. The gang wakes up later and finds Mrs. Grubwort, who says that her evil ancestor has possessed Velma.
Shaggy is heartbroken, though Fred tries to sympathize, saying that he wasn't the only one whose first love was now an evil witch. The gang realizes that they missed all the little signs - the warts, Velma's fear of fire, her love of moonstones, and how she spilled the tea on the video of the witch because it was going to show her face - that should have proved Velma was up to something, but they were too absorbed with all their side problems. The woman says that Wanda probably would have gone to the caves. Shaggy, remembering a bit of information Velma had given him, points out that they're underwater, so the woman offers to rent them scuba gear. They arrive in the cave and while hiding, see Wanda turn several more frogs into monsters. Shaggy bursts out of hiding and commands Velma to stop. Wanda sets her monsters on the gang, and while Scooby, Fred and Daphne run for their lives, Shaggy stays back and tries to help Velma fight the witch. He briefly reaches her by telling her about his feelings, but Wanda takes over again and pins him to the wall.
Meanwhile, Fred and Daphne reach a dead end. Both fearing that it's the end, they apologize for the fights that they had. The lake monsters then burst through the wall. At the same time, Shaggy tries once again to save Velma by singing her favorite song. Velma joins in, and manages to break free of the witch's control. The ghost of Wanda tries to grab her staff, but Scooby Doo arrives just in time and smashes it into a rock, destroying Wanda. Fred and Daphne, who are about to be killed and are clutching one another for dear life, see the monsters turn back into frogs, They run back to Shaggy, who is confessing how much he really likes Velma. Both Fred and Daphne impatiently tell him to just kiss her. Velma and Shaggy kiss, but afterwards both agree that they didn't feel a single spark, and it's better if they're just friends. Fred and Daphne agree as well that all of them are meant to be just friends.
The next day, Uncle Thorny tells the gang that they are so many applications for membership that he wasn't sure if he could take everyone, and gives the gang $10,000 to take care of the damage done to the barn. He also says that he will call his attorney and see whether the gang can incorporate, to take care of any future damage.
Daphne suggests Mystery Incorporated for their sleuthing group name and they all agree as they do a group hug - except for Scooby, who is still upset with Shaggy. Scooby wanders away, but falls over the balcony railing and is caught by Shaggy, who assures Scooby that he [Shaggy] will always be there for him, and all is well.
- Robbie Amell as Fred Jones
- Kate Melton as Daphne Blake
- Hayley Kiyoko as Velma Dinkley
- Nick Palatas as Shaggy Rogers
- Frank Welker as Scooby-Doo (voice)
- Ted McGinley as Thornton "Thorny" Blake V
- Richard Moll as Elmer Uggins
- Marion Ross as Mrs. Trowburg
- The Lake Monsters
- Wanda Grubwort
- The Vengeful Scarecrow from "The Frickert Fracas"
The film was released on DVD through Warner Home Video on March 1, 2011. Warner Bros. Home Entertainment distributed the film on Blu-ray Disc.
The television premiere drew 3.4 million viewers, a little over half of the 6.1 million with which the first film premiered.