That night, Harry gathers the golden egg and the Marauder's Map, and in his Invisibility cloak, he sneaks into the prefects' bathroom. It is extraordinary: there are piles of fluffy towels, walls of white marble (one of which holds a painting of a beautiful, sleeping mermaid), and a swimming-pool sized tub with hundreds of jeweled taps that spurt out various kinds of bubbles. As soon as Harry has undressed and gotten into the water, he is joined by Moaning Myrtle, who suggests that he listen to the egg underwater. He does this, and he hears a song telling him to find something he has lot underwater. He deduces that he must reclaim something from the mer-people in the lake. As he thanks Myrtle and returns invisibly to his room, he notices on the map that Bartemius Crouch is inside Snape office. In surprise, Harry steps on the trick stair, getting his foot stuck and dropping both the egg and the map.
Filch appears and grabs the open and scratchily singing egg, thinking it is some doing of Peeves. Soon Snape appears and accuses someone of having been in his office. Before anything else can happen, Moody arrives, and his mad eye is clearly able to see Harry under his cloak. Moody figures out what is happening and he takes the map and the egg, and he sends the other two observers off to bed. Then he asks Harry, who has removed his cloak, whom the map showed in Snape's office, and Harry replies that it is Mr. Crouch. Moody seems alarmed, mentions that odd things have been going on lately, and asks if he can borrow the map, which Harry agrees to let him do. As they head up to bed, Moody says that Harry is a sharp boy, and tells him to consider a profession as an Auror.
The next day in class, Harry confides everything to Ron and Hermione. They speculate on whether Moody or Mr. Crouch has been hired to keep an eye on Karkaroff and Snape. That night, Harry sends a letter to Sirius, updating him; he responds, wanting to know the date of the next Hogsmeade visit. Harry writes back, telling him when. Harry, Ron, and Hermione do not know how Harry can survive for an hour underwater. Hagrid returns to teaching, and he seems deeply confident that Harry will win the tournament.
The evening before the second task, Harry spends the night in the library, poring through books that could offer help; he is alone, because Ron and Hermione have been mysteriously summoned away to Professor McGonagall. Harry drifts into sleep and is awakened ten minutes before the second task by Dobby, who offers him a ball of something called gillyweed, which supposedly will allow him to breathe underwater. Having no other alternative, Harry runs down to the lake, eats the gillyweed, and dives into the water with the other three champions.
Harry grows gills, and can swim quite easily. At the bottom of the lake he finds the village of the mer-people, and he sees Ron, Hermione, Cho, and a girl who must be Fleur's younger sister, all asleep and tied together. Harry uses a rock to free Ron, and he waits to see if the others will be rescued. Cedric eventually comes for Cho, and Krum for Hermione, but Fleur never arrives. So Harry fends off the ugly, broken-toothed, oddly-colored, aggressive mer-people with his wand, and carries both Ron and Fleur's sister to the water's surface. He is the last to arrive, and he feels foolish for waiting around underwater when he could have come up first. A mermaid swims to the surface and informs Dumbledore that Harry was the first to arrive, but waited to make sure all four hostages were rescued, so Harry receives very high marks from the judges on his completion of the second task. Fleur is grateful and kisses both Ron and Harry. Hermione is so preoccupied with Harry that she ignores Krum as he plucks a water-beetle from her hair. Harry is immensely grateful to Dobby, and plans to buy him pairs and pairs of socks.
Harry's success is a result of other people's help in these chapters. Outside assistance is especially important as he enters the lake, previously unexplored territory, opening up yet another level of exploration to Harry's Hogwarts experience. Moody becomes more of a conspirator with Harry during the invisibility cloak sequence on the stairs—causing Harry to wonder why Moody is so suspicious of Snape, and causing him to entrust Moody with his precious Marauder's Map.