Harry looked at the others in shock. He hadn't expected this; and yet, he thought ruefully to himself – and yet it made sense. They hadn't seen Dumbledore; they'd only heard him through the door to his study.

"How did you know to come looking for us?" he asked, as the feeling of relief they'd all had on meeting each other dissolved and the need to escape became more concentrated. They started walking again, Hagrid and Lupin in front, then Snape, and then the rest of them scuttling along behind them. Hermione's illuminatus spell was being propelled along in front of them by her wand, but this was the only source of light they had; Harry stumbled over his robes in an effort to keep up with Sirius's long strides and hear what he had to say.

"Well – we got back an hour ago, as I said, and only realised you were gone when Hagrid went to fetch you from the dormitory and found you weren't there. Dumbledore seemed to realise that something had happened: he sent us after you – a hard job, I'll admit, without the Marauder's Map – and he should be following us now. He had something he had to do first. But I don't think any of us had quite anticipated this happening. Tell me – what are you doing down here, Harry?"

Harry quickly filled him in on the night's events.

"But what happened with your wands?" he asked, when he had finished. "Who put the mute charms on you?" He stepped through a heavy black door and into a slightly wider tunnel, where he could walk two abreast with his godfather.

Sirius sighed. "That was Voldemort," he said. "Yes," he added, as Harry started at the name, "I know. We were remarkably foolish… none of us had guessed that he was actually in the building; Lupin and I reached the secret tunnel, and suddenly were confronted by Voldemort: he took our wands, then disappeared. I'm not sure why – maybe he heard Snape and Hagrid behind us. Anyway… next time we tried to talk we all found that we couldn't, and I'm pleased that one of you, at least – " Harry could have sworn that Ron and Hermione both blushed in the dark – "Could read lips. I honestly don't know what Voldemort had hoped to achieve by silencing us rather than killing us: maybe he wants us alive for something. I don't know."

Harry shivered. Nothing was making sense at the moment. They continued for a while in silence, and he tried to sort through his tangled thoughts.

Who was it they'd heard pretending to be Dumbledore? Why hadn't his scar hurt if had been Voldemort? Who else was there in the castle? Filch? Dobby? Professor McGonagall? Madam Pomfrey? Harry laughed silently to himself. All these seemed impossible candidates for Dumbledore impersonators. Had somebody been drinking Polyjuice potion? Maybe – and fear struck straight at Harry's heart as he thought it – maybe the Dumbledore they'd been seeing and speaking to since they'd arrived hadn't really been Dumbledore at all. He rubbed his aching head. He couldn't puzzle it out.

He had been thinking so intently that he walked into Ron's back before he realised that they'd stopped. Again, he put a hand to his head: it had begun to sting. Fingering his scar gingerly, he wondered vacantly why Ron wasn't moving.

"What's happened?" hissed Snape's voice. "Lupin, why have we stopped?"

There was no reply from Lupin, and Harry looked over his shoulder with a cold dread beginning to form in his stomach. He had no doubt any more as to why they'd stopped. His scar was now throbbing with an intensity that nearly knocked him off his feet.

Suddenly, he turned and started towards the door they'd just come through, but it shut with a clang; thick vines began to grow quickly around it, groping the wood with their long tendrils and suffocating the lock. In despair, Harry spun round again to evaluate their chances of escape from the room they were in at the moment: but it seemed to be a dead end. He could see no other door in the place except one right at the top of a long set of stone steps similar to the ones at the beginning of the secret passage he, Ron and Hermione had fallen down earlier.

The only difference in this case was that whereas the first flight had been empty, this one had someone standing at the top looking down at them.

It was Voldemort. They were trapped.