Muscle Man has been building a water slide for six weeks, while Mordecai and Rigby watch him. They want him to go down the slide already, but he refuses to go, saying it isn't ready yet. They start teasing him until he finally agrees to go down the slide. It starts good at first, but then the support beams of launch ramp he was building collapses, so he ends up hitting his trailer and flies into a tree, hitting many branches, and finally landing on Muscle Man's car. Muscle Man is in really bad shape, but claims he is all right. Suddenly, Death shows up on his motorcycle talking on his phone about a babysitter who is unable to babysit for him. Death tries to claim Muscle Man's soul since this counts as his death, but Mordecai and Rigby refuse to let him, saying that they will do anything. Death agrees to the duo's bargain, and says he will spare Muscle Man's soul if they agree to babysit his kid while he and his wife go out to dinner for their anniversary. The duo agree to babysit Death's kid, but then Death puts Muscle Man inside a small amulet that is held by Mordecai and Rigby. He tells them if they fail, Death will claim Muscle Man's soul.
The group goes to Death's Manor where they meet his four-armed wife. She questions Death on how he obtain these "babysitters" and their skills on taking care of paranormal children. Mordecai and Rigby are then introduced to his baby son, Thomas. Death's wife tells them that if Thomas is not asleep when they get back, she'll be disappointed in all of them and Death tells Mordecai and Rigby he'll be especially be disappointed, too. Muscle Man questions Mordecai and Rigby is they even know how to put a baby to sleep but they tell him it will be easy.
They try to put Thomas to bed already, but Thomas reveals his intellect and he can talk. Mordecai asks him if his parents are aware of this which he reveals he keeps it a secret and is milking this baby care for while. He says that he will not go to sleep unless they play with him. However, playtime ends up insane when Thomas rips apart his dolls, shoots darts toy at Mordecai and Rigby, and almost sets the house on fire.
After playtime, they try to get Thomas to go to sleep again, but he refuses to sleep unless he eats. Mordecai tries to give him a glass of warm milk, but Thomas refuses to drink it and instead eats up an entire jar of cookies and a bag of sugar, which makes him go hyper and destroy some of the kitchen.They get a call of Death telling them that they're coming back. Soon enough, Thomas disappears and they go looking for him. They find him in the library where he asks them to read him a story. Mordecai tries reading him a story back Thomas wants them to read him a story called the "The Hungry, Hungry Soul-Sucking Death Worm", which they are hesitant at first. At the end of the story, Thomas has Mordecai and Rigby pull the last picture tab in the book, where the Soul-Sucking Death Worm from the book comes to life.
The worm wants to eat a soul and won't go back into the book unless it does so and the only soul in the room is Muscle Man's. Mordecai and Rigby try to prevent this, but Thomas wants to feed the worm Muscle Man's soul. The worm destroys much of the house. Rigby comes up with a plan to trick the worm into going back in the book by throwing the amulet of Muscle Man to Thomas where the worm leaps toward him. Rigby jumps in front of him with the book which the worm goes back in the book, but not before getting temporary caught on a glass chandelier.
After the trouble has ended, they try to put Thomas to bed yet again, but Thomas refuses after they ruined his story time and almost got him killed. As Death and his wife approaches the door, Thomas starts laughing thinking they have failed. However, the chandelier that was loosen by the worm drops and lands on Thomas, knocking him out before his parents enter.
Death and his wife soon come in and are aghast to find their house wrecked. When Death's wife sees Thomas is asleep. Death thanks Mordecai and Rigby for watching Thomas, and releases Muscle Man from the soul amulet. Death then tells them they shouldn't think that he will spare their souls next time, because Muscle Man will soon get himself killed at a hot dog eating contest. Afterwards, the trio try to wonder how they will get home.
This episode provides examples of:
- Arson, Murder, and Jaywalking:Mordecai: (looking through Death's fridge) Okay. Soul juice, goat's feet, aaaww... almond milk?!
- Arson, Murder, and Lifesaving: Death was mad at Mordecai and Rigby for having their furnitures broken, fires spreading all over the place, and his favorite harp ruined and on fire. But when he sees that Thomas is asleep and his wife happy about it, he declares Mordecai and Rigby the best babysitter they ever had.
- Babysitting Episode: Mordecai and Rigby has to babysit Death's son, Thomas, in order to save Muscle Man's soul.
- Baby Talk: Thomas does this only when his parents are around to keep up the charade that he's still young.
- Badly Battered Babysitter: Mordecai and Rigby, as a result of having to babysit Death's son.
- HA HA HA No: Death gives this responds when he tells them that Muscle Man is going to die in a hot dog eating contest (even though that did come true later on the episode "Last Meal").
- Laser-Guided Karma: Thomas gloats that Mordecai and Rigby are too late to put him to sleep when Death and his wife are about to arrive but a glass chandelier drops on him which knocks him out cold.
- Manchild: Despite Thomas's age, he sometimes acts like a infant.
- Montage: There's one where Mordecai and Rigby are playing with Thomas and they see how dangerous he can be.
- Oh, Crap!: Mordecai's and Rigby's reactions to Muscle Man's water slide accident and a glass chandelier dropping on Thomas.
- Parental Obliviousness: Death and his wife has no idea that Thomas can talk and his true age. They don't even question why he was under a chandelier when it dropped on him.
- Really 700 Years Old: Thomas is 300 years old.
- Tempting Fate: When Mordecai and Rigby thinks it's going to be easy taking care of Thomas.
- Tome of Eldritch Lore: The book, The Hungry Hungry Soul Sucking Deathworm.