Is the trio's Polyjuice escapade in Chamber of Secrets ever discovered?

Question

In HP and the Chamber of Secrets, Harry, Ron, and Hermione "break about fifty school rules" by brewing Polyjuice Potion and drugging and impersonating other students, just in order to get into the Slytherin common room and probe Malfoy for information about the Chamber of Secrets.

Is this little adventure ever discovered by Those in Charge (teachers)? Or even by Malfoy?

If so, did they ever get punished? I can't see how they could fairly have avoided it (other than they're the Golden Trio and always do). In the end they don't actually get any useful information, except that Malfoy isn't the culprit. This escapade doesn't help them at all in their eventual discovery of the culprit and destruction of the Basilisk. It was just motivated by their suspicion of Malfoy, which was essentially based on "he's Slytherin and we don't like him" and turned out to be unfounded.

If not, how could it remain undetected? Hermione's skill with Polyjuice Potion is eventually common knowledge ... more importantly, why didn't Crabbe and Goyle run to tell someone when they woke up and found they'd been drugged? Did the topic never come up between Malfoy and the pair of them, with Malfoy realising he'd been talking to impostors? What did they tell Madam Pomfrey about Hermione's semifelinity after her failed attempt to Polyjuice herself into Millicent Bulstrode?

Answer 1

Do the teachers find out?

Snape works out part of their crime. Others might work it out as well.

When they steal the Polyjuice ingredients, they let off a firework in his classroom. He's bound to realise which ingredients were stolen, and what they were likely used for. Given that Hermione's feline appearance was public knowledge:

So many students filed past the hospital wing trying to catch a glimpse of [Hermione] that Madam Pomfrey took out her curtains again and placed them around Hermione’s bed, to spare her the shame of being seen with a furry face.

— Chamber of Secrets, chapter 13 (The Very Secret Diary)

I'm sure Snape is able to put it all together – somebody has been trying to make Polyjuice, Hermione has had a botched transformation, Hermione probably tried to make Polyjuice. And since the trio operate as a single unit, Harry and Ron were probably involved as well.

In Harry's fourth year, we get confirmation that Snape suspected something funny, but was apparently unable to prove it:

Harry stared back at Snape, determined not to blink or to look guilty. In truth, he hadn’t stolen either [Boomslang skin or Gillyweed] from Snape. Hermione had taken the boomslang skin back in their second year — they had needed it for the Polyjuice Potion — and while Snape had suspected Harry at the time, he had never been able to prove it.

— Goblet of Fire, chapter 27 (Padfoot Returns)

Unless other teachers knew that Snape's stores had been raided, and what exactly had been stolen, it would be much harder for them to work it out unless he told them.

However, I don't recall any indication that Snape knew why they were making Polyjuice. For example, he never seems to suspect they were infiltrating the Slytherin common room.

Were they ever punished? If not, why not?

I don't recall any punishments.

The most serious (known) crime would be stealing from Snape's stores, something he was never able to prove. McGonagall would object if Snape inflicted major punishment based on an unproven crime.

And even if he can prove that Hermione has taken Polyjuice, she could have obtained the ingredients and/or potion itself from elsewhere. (A plausible line of thinking is that Hermione ordered dodgy Polyjuice via mail order, and that's why she looks like a cat.)

Apparently Madam Pomfrey isn't a source of probing questions:

“It’s okay, Hermione,” said Harry quickly. “We’ll take you up to the hospital wing. Madam Pomfrey never asks too many questions….”

— Chamber of Secrets, chapter 12 (The Polyjuice Potion)

She probably knows that Hermione was using Polyjuice – so that she can treat her – but again, not why or how.

Given that Hermione is ridiculed by her peers and looks like a cat for a week, some may also consider her sufficiently chastised that she's unlikely to try experimental potions again in a hurry. Why punish her further?

Did Malfoy ever work it out?

Seems unlikely. When Harry and Ron are chatting with him, he doesn't seem to rate Crabbe or Goyle's mental prowess:

“What’s the matter with you two?”

Far too late, Harry and Ron forced themselves to laugh, but Malfoy seemed satisfied; perhaps Crabbe and Goyle were always slow on the uptake.

— Chamber of Secrets, chapter 12 (The Polyjuice Potion)

The whole episode could be written off as extreme dopiness. If they stumble in later claiming they were drugged, what's more likely – they were actually drugged, or just having another moment? There are plenty of other plausible reasons they could be knocked out for a few hours – Weasley twins, Peeves, bumbling incompetence – that don’t involve foul play. Hanlon’s razor, etc. I don’t think they ever realised something had happened.

Even if they noticed, it would be hard for them to say something which would get Malfoy really suspicious. And by the time he learns about Polyjuice in years to come, I don't think this episode would stand out enough to be unusual.

If Malfoy ever suspected impostors in the Slytherin common room (especially the trio), he would raise merry hell about it, whether or not he could prove it. The fact that he never mentions it seems suspicious.

Answer 2

Snape always suspected, and actually accuses Harry of stealing Polyjuice supplies from his storeroom in Goblet of Fire (falsely, this time; Moody was the one stealing the supplies):

I give you fair warning, Potter," Snape continued in a sorter and more dangerous voice, "pint-sized celebrity or not - if I catch you breaking into my office one more time -"

"I haven't been anywhere near your office!" said Harry angrily, forgetting his feigned deafness.

"Don't lie to me," Snape hissed, his fathomless black eyes boring into Harry's. "Boomslang skin. Gillyweed. Both come from my private stores, and I know who stole them."

Harry stared back at Snape, determined not to blink or to look guilty. In truth, he hadn’t stolen either of these things from Snape. Hermione had taken the boomslang skin back in their second year - they had needed it for the Polyjuice Potion - and while Snape had suspected Harry at the time, he had never been able to prove it.

^{Goblet of Fire Chapter 27: "Padfoot Returns"}

However, he apparently could never prove anything; the incident is never brought up by any other authority figures over the course of the series, and they're never even threatened with punishment for it (except by Snape).

As to how it was never discovered; there doesn't actually appear to be any reason to suspect it could be discovered:

• As far as we know Hermione never makes Polyjuice again (she steals the stuff they use in Deathly Hallows). Although she's able to identify it in Slughorn's potions class in Half-Blood Prince, that's no reason for anyone to be suspicious; knowing things above her grade level is Hermione's defining character trait
• Crabbe and Goyle have no reason to believe they weren't simply the victim of a prank; with the Weasley Twins running amok, the school is most likely used to them by now

• We don't know how long they were awake in the cupboard Harry and Ron locked them into, or how long they were stuck in there before they got out; all we get is:

  Harry could feel his feet slipping around in Goyle's huge shoes and had to hoist up his robes as he shrank; they crashed up the steps into the dark entrance hall, which was full of a muffled pounding coming from the closet where they'd locked Crabbe and Goyle.

  ^{Chamber of Secrets Chapter 12: "The Polyjuice Potion"}

  It seems unlikely that they'd been awake long; if you're going to impersonate someone with a potion you know lasts for exactly an hour, why would you render them unconscious for any period of time shorter than an hour? With the amount of detail that went into this plan, that seems like an improbable oversight.

  What's more, they obviously can't get out on their own, or not easily. If neither of them noticed their watches suddenly jump an hour, they and Malfoy would have no reason to be suspicious

• If one of them did notice the time difference, is there any reason to think Malfoy would believe them? It's pretty clear from Harry and Ron's conversation with him that Malfoy doesn't think highly of his "friends'" intelligence; it could easily be rationalized as them getting confused, or distracted, or losing track of time in the Great Hall

• Finally, even if either Crabbe or Goyle noticed the time gap, and even if Malfoy believed them and they went to Snape (who had his own suspicions), what connects the incident to Harry, Ron, and Hermione? Crabbe and Goyle never saw Harry or Ron, and Snape has no proof they were involved in stealing from his stores. The only evidence they have is that Hermione (entirely legitimately) checked out a book that happens to contain the recipe for making Polyjuice Potion, shortly before several of the ingredients were stolen from Snape's store room and Malfoy suspected someone of impersonating Crabbe and Goyle.

  Although that's certainly an abundance of coincidence, there's no proof of involvement, especially when all parties have a well-documented mistrust of one another

• The issue of Madame Pomfrey is hand-waved in the book:

  "It's okay, Hermione," said Harry quickly. "We'll take you up to the hospital wing. Madam Pomfrey never asks too many questions..."

  ^{Chamber of Secrets Chapter 12: "The Polyjuice Potion"}

  It doesn't seem like it would be difficult to come up with an excuse that would satisfy her; in a castle filled to the brim with still-maturing students, all of whom have immediate access to reality-warping powers, I shudder to think what she considers a "normal" injury