The Egg and the Eye
Chapter 25 of Harry Potter and the Goblet of Fire: The Egg and the Eye
On Thursday night, Harry sneaks out of Gryffindor Tower with his Egg and heads for the Prefects' Bathroom, armed with his Invisibility Cloak and the Marauder's Map to avoid being caught again by Filch for breaking curfew. The bathroom is luxuriously decorated in white marble and contains stacks of fluffy towels and a pool-sized tub with hundreds of jeweled taps that spew many-colored bubbles. On the wall is a painting of a beautiful mermaid. Harry slips into the water and plays with the taps a bit before opening the Egg. It wails horribly. He slams it shut and is startled by Moaning Myrtle, who suddenly appears, sitting on the tub's edge. She suggests putting the Egg in the water. Once Harry is submerged, a faint singing is heard. Dunking his head, Harry hears the Egg singing about something he will sorely miss that will be at the bottom of the lake. He will have only one hour to find it. Harry guesses that there are Merpeople in the lake, which Myrtle confirms. She is upset when Harry ponders how he will be able to breathe underwater, saying that nobody remembers that she can't breathe any more.
Harry gathers the Egg and his other belongings and, covered by his Cloak, prepares to head back to Gryffindor tower. The Map shows no one is in the halls except Peeves. Someone is in Professor Snape's office: Bartemius Crouch. Harry wonders why Mr. Crouch is at Hogwarts so late, particularly as he is apparently ill and was unable to attend the Yule Ball. Harry decides to investigate, but as he is concentrating on the map, his foot becomes trapped in a trick step, causing him to drop the Egg and the Marauder's Map. The Egg rolls down the staircase and starts wailing, summoning Filch who in turn yells at Peeves, assuming the Poltergeist had stolen a Champion's Egg. Snape arrives and dismisses Filch's accusations about Peeves, and claims someone broke into his office. It had to be a wizard; Snape seals his office with a Charm to prevent Peeves from entering. Professor Moody appears and is concerned that someone was in Snape's office. Moody's magical eye spots Harry under his Cloak, but says nothing and offers to help Snape investigate the break-in. Snape demurs, saying he believes it was a student stealing potion ingredients. Moody wonders if Snape could be hiding something else, to which Snape retorts that Moody has previously searched his office. Moody says that it is an Auror's privilege. Although Dumbledore may have faith in Snape's loyalty, Moody is less trusting. Moody dismisses Snape, causing Snape to bridle. Moody then spots the Marauder's Map on the floor which Snape immediately recognizes. Harry, under his Invisibility Cloak, gesticulates madly to Moody that it is his. Moody summons the map from Snape's fingers over to him. Snape, furious, probes the air searching for Harry hiding under his cloak. Moody claims nobody is there, though he thinks it curious how quickly Snape's thoughts turned to Harry. Detecting a threat, Snape departs. Filch, protesting that the Egg is evidence, reluctantly hands it over to Moody and leaves.
The map fascinates Moody, who is seemingly unable to keep either eye off it. He helps Harry from the trap step and asks if the map showed who was in Snape's office. Harry replies it was Mr. Crouch. Moody is amazed, and explains that Crouch is obsessed with catching Dark wizards, far more than Moody himself. Moody asks to borrow the map. Harry, deeply relieved he does not have to explain where he got it (and thereby implicate Fred and George), agrees. As he goes into his office, Moody suggests that Harry consider becoming an Auror. When Moody asks if Harry was just taking his Egg for a stroll, Harry says he was working out the clue. Later, Harry thinks he would like to see how badly scarred other Aurors are before choosing that career path.
Several important things should be noted: one, Bartemius Crouch, who was too ill to attend the Yule Ball and sent Percy Weasley in his place, is apparently well enough to travel to Hogwarts and root through Snape's office. Another is the Egg and its song; solving the Egg's riddle only leads to yet another problem for Harry—how to breathe underwater for one hour. The Tournament is now only a few weeks away, and Harry's procrastination in solving the riddle has wasted much valuable time; he will need help and have to work especially hard if he is to solve this next crucial step in time.
Additionally, there is Professor Moody's odd behavior when he spots the Marauder's Map. He is intensely interested in it, staring fixedly at the parchment when he realizes what it is, and then borrowing it from Harry. Just as Professor Lupin had in Harry Potter and the Prisoner of Azkaban, Moody's timely intervention prevents Snape from punishing Harry. Here Moody shows his unconventional personality, and, as he has previously demonstrated, he is far less concerned about rule breaking than either Filch or Snape. This trait has helped make him a popular teacher, though his actions here may have as much to do with his ongoing enmity with Snape as it does with protecting Harry. Also like Lupin, Moody prevented Snape from confiscating the Marauder's Map, scooping it from his grasp with the Summoning spell. Some readers may wonder why Harry failed to do the same; he had his wand, attempting to blank the map with it when Filch appeared. It seems likely that Harry, with the Egg screaming and Filch rapidly approaching, may simply have panicked. One can imagine the words "Why didn't I remember that?" flashing across Harry's mind when Moody cast the Summoning charm. This particular charm had proved especially difficult for Harry to learn, however, and he may still be having some trouble using it, particularly under duress. Harry's gratitude to Moody is such that he readily agrees to loan him the map, though Harry is probably wondering just why and how Moody intends to use it.
- Why does Moaning Myrtle help Harry with the Egg?
- Why is Myrtle upset about Harry's next Triwizard task? How will Harry overcome this obstacle?
- Why did Snape suspect that Harry was involved in the ruckus in the hallway? Even though Harry was there, were Snape's suspicions justified or was it his usual rush to judgment where Harry is concerned?
Further Study 
- Why would Mr. Crouch be in Snape's office so late at night?
- Why would Moody have previously searched Snape's office?
- Why does Moody hide Harry's presence from the others in the hall?
- Why does Moody want to borrow the Marauder's Map? Why does Harry agree to let him use it?
- Why does Moody suggest that Harry become an Auror? Explain why you agree or disagree. What is Harry's reaction?
Greater Picture 
The Marauder's Map's power once again strips away disguises; in Harry Potter and the Prisoner of Azkaban, it correctly spotted Peter Pettigrew when, in his Animagus form, he was disguised as Scabbers. In this case, it showed "Bartemius Crouch" in Snape's office. Of course, it was the false Moody collecting ingredients to brew more Polyjuice Potion. While the Marauder's Map correctly gave his name, it is apparently unable to differentiate between Bartemius Crouch Sr., and Bartemius Crouch Jr., who is using the Polyjuice Potion to impersonate Moody. However, this is a clear indication that Polyjuice potion cannot fool the map, any more than it is deceived by Animagi.
This explains Moody's interest in the map, and why he is so keen to borrow it: apart from it being a useful tool that shows everyone's whereabouts at the school, it can also expose him as an impostor. It was imperative to get the map away from Harry to conceal his true identity. There may have been an even more immediate need for Moody getting the map into his possession: the map was revealing that it was Barty Crouch standing directly opposite Harry rather than the real Mad Eye Moody. Moody's suggestion that Harry become an Auror may have been intended as flattery to distract Harry's attention away from the map and also deflect questions as to exactly why Moody would want the map. Whether or not Moody's flattery was genuine, Harry is indeed well-suited to becoming an Auror, Defense Against the Dark Arts being his best subject, something Barty may realize he needs to be cautious about. Also, it does seem that if Harry were a little more observant, he might noticed on the map that the real "Mad Eye" Moody never appears to leave the Defensive Arts instructor's living quarters (where he is being imprisoned) or that Barty Crouch is often in places and at times when only Mad Eye Moody should be there.
In a later chapter, Sirius claims Snape was never accused of being a Death Eater; this is actually incorrect, Snape was accused, but Dumbledore vouched for him. It was Moody who arrested Snape, and who is probably still suspicious that he is a Death Eater; the false Moody will display this same belief in order to be true to his model, and to avoid making Dumbledore suspicious. Karkaroff is a known Death Eater, Sirius mentioned that just before the first task. If Snape was or still is a Death Eater, as Ron, Harry, and to a lesser extent Hermione suspect, that would explain why he and Karkaroff were on a first-name basis at the Yule Ball.
Finally, it is unknown whether Barty Crouch, Jr. actually knows if Snape was a Death Eater. It is learned at the end of this book that Snape bears the Dark Mark, which not only brands Death Eaters, but also acts as a summons from the Dark Lord. In the second chapter of Harry Potter and the Half-Blood Prince, we learn that Snape was not only a Death Eater, but was in Voldemort's inner council. Considering how young Barty was when he was imprisoned, it is possible that he was never directly connected with Voldemort, but only associated with the Dark Lord's supporters after Voldemort himself was gone. If so, he might have learned that Snape was in Voldemort's inner council from Bellatrix Lestrange or her associates, or possibly, more recently, from the true Alastor Moody. Barty is likely unaware that Dumbledore vouched for Snape's allegiance, but he would immediately see that Dumbledore had complete trust in him despite his Dark history.