Except, of course, it was nowhere near that simple. Hogwarts was in lockdown. Other than for lessons and meals, students couldn't leave their common rooms at all. This was all perfectly understandable and sensible and all that (except for the little voice in his head which told him Slytherin's monster could just kill everyone at once this way) but it was very frustrating for Leo in several ways.

Quite apart from his instinctive hatred of any restrictions on his personal freedom, it made it an awful lot harder for him to follow up the one lead he had on the whole mystery: there were no opportunities to speak to Potter.

The latest news didn't exactly cheer him up: Hagrid had been arrested and sent to Azkaban and Professor Dumbledore had been suspended as Headmaster. From the smile on Draco's face, Leo got a strong sense that Lucius Malfoy had something to do with this.

In the end, after a week's frustration which practically drove him insane, he cornered the Boy-Who-Lived at the end of Double Potions.

"I need to know about the diary," he said urgently, as they were led by Professor Snape out of the dungeon.

"What diary?" asked Potter. Leo couldn't tell if this was genuine confusion or if he was bluffing.

"The fifty-year-old diary," said Leo impatiently. "The one in your bag on Valentine's Day. Draco might be blind, but I'm not. It's important in some way. I need it."

"Even if I wanted to give it to you, which I don't," said Potter, "I can't, because it's been stolen."

Leo tried not to show his astonishment. "When?" he asked quickly. "No – wait – don't tell me – the day of the last attacks." It was only a hunch, but it was correct.

"How did you know that?"

"Guessed," replied Leo. Another idea had sprung to mind. "That voice you've been hearing in the walls – what's it been saying?"

"Why – wait – can you read minds or something?"

Leo smiled to himself. Another suspicion confirmed: Slytherin's monster was a snake of some kind. Marisa had been right. He made a mental note to thank her when she woke up. "Can you at least tell me about the diary? Whose is it? What does it say?"

But before Potter could decide whether to answer, they arrived at the Charms classroom and Leo had to file in with his fellow Slytherins, away from any chance of getting what he needed.