After watching the Unsolvable Mysteries TV show, Grim realizes he forgot a million years ago to reap the Abominable Snowman living in the Himalayas. Billy, Mandy and Grim go there to finish the job and also to obtain videographic proof of the snowman's existence. The Yeti, who likes to be called Abom, manages to escape Grim more than once before finally being trapped by the moving glacier. Grim watches the TV show again, but he may have forgotten to reap the Loch Ness monster too.

A scene of Endsville two weeks into the future shows a dystopian world ruled by the "Lord of Horror", who wields the all-powerful artifact known as "Horror's Hand". At the same time, two robotic replicas of Billy and Mandy are sent into the past, to stop the real Billy and Mandy from interfering with the current events.orror's Hand to rule the world.

On a rainy day, giant spiders appear in Billy and Mandy's school and start kidnapping the children one by one. Grim presumes this is somehow related to his past, but does not figure it out until he receives a message saying that Velma, the Spider Queen, an old good friend from high school, is responsible for it. Meanwhile, Billy meets with Jeff the Spider, who informs him that he is precisely marrying Velma. After trying to recover a talking carton of chocolate milk from Jeff, Billy and Jeff get into a fight, and Jeff looks angrier than ever before.

When Billy, Mandy and Grim go to a joke shop, they find the owner is former boy wizard Nigel Planter, who reveals that his powers diminished and was kicked out of Toadblatt's School of Sorcery. Planter steals Grim's scythe and heads to the school to exact revenge on those who wronged him. The guys seek the help of Planter's sworn enemy, Lord Moldybutt, to find the school. Grim recovers his scythe, and Moldybutt turns out to be in fact only a real estate agent, who informs Planter that he is the heir to the "Peanuts by Planter" farming company.