Meanwhile, Harry had once again been denied sleep – this time by Hermione, who had got bored without her usual entertainment means of the library.

"Can't you all just leave me alone?" snapped Harry, well and truly annoyed at being disturbed yet again.

"Oh, Harry," said Hermione, equally impatiently. "The food'll be ready in a minute, and you're not doing much lying down there, are you? We ought to offer to help."

"Thought you were all set against female labour in the kitchen," retorted Harry, resignedly giving up all hope of sleep. He was exhausted.

"Well – " started Hermione, looking exasperated – but was interrupted by a snap of twigs, and they both looked up. Ron was walking towards, them, looking rather dazed.

"What on earth's the matter with you?" exclaimed Hermione anxiously.

"Snape just – he just – " Ron stuttered, still not having quite lost the look of a rabbit staring the encroaching headlights of a car full on.

"Snape just what," growled Harry.

"He just – just smiled at me," said Ron, sinking into the ground.

"Are you sure he wasn't just baring his teeth to try and bite you or something?" asked Hermione doubtfully.

Ron considered, but finally shook his head. "No," he said. "That was a definite grin. Even if it was a Snape one. Lupin was right."

Hermione and Harry stared at their friend cynically, then shrugged at each other.

"He has been under a tremendous amount of strain lately," reasoned Hermione. Harry nodded, sagely, and Ron frowned at them both.

"You try being nice to him, then," he snapped. "He was being all right to you earlier, Harry. Why don't you go and pick him some flowers or something Hermione – or do you reserve that for Victor Krum?"

Hermione spared Ron a purely evil glance, and Harry hastened to interrupt.

"Come on," he said. "Let's – er – let's go and eat, shall we?"

The next day dragged on as slowly and painfully as the first: before long, everyone had given up any attempts at conversation, as all their breath was needed for continuing in a straight line without falling over.

"I – can't – take – much – more – of – this – " panted Ron, looking horribly red in the face. "Think I'll just fall over here, and… and go to sleep." And, much to Harry's alarm, he did just that.

"Sirius!" he yelped, panicking. "Ron just collapsed! He's – what's wrong with him? Sirius! What's wrong with you?"

He looked about him. Everyone seemed to be growing steadily drowsier, their eyes drooping and knees swaying. Hermione fell to her knees with a crunch.

"Hey!" said Harry. "What are you all playing at? What's the matter?"

He ran over to where Snape was just beginning to fall asleep, his head resting dangerously close to the edge of a small stream that they would have to ford if they wanted to continue in the right direction. Harry nudged it away with his foot.

"Somebody!" he shouted. He fingered his wand, wondering whether it would be safe to use magic: but he remembered Lupin's words of warning, and thought wildly. There had to be some other way. What was happening?

And then something horrible happened. The stream in front of him seemed to bubble, like hot water: something spun round, and round, and round in it, making Harry feel dizzy and confused.

"What're you?" he asked in a thick voice, as a figure emerged from it. It was a very odd-looking figure: the lower half of its body was human, but covered in thick, green fur: the upper half was like that of a horse's. And the eyes, which were now staring at Harry – the eyes were that of a goat's. Harry forced his brain to think, and dredged up all the Defence Against Dark Arts lessons he could remember – and then it clicked: this was a Selkie.

"What've you done to them?" he asked angrily, gesturing at his companions who lay, sprawled, in various uncomfortable-looking positions. To his relief, Ron had begun to stir again, and was now on his knees.

"They are sleeping," replied the Selkie, in a voice that sounded like several nails being scraped down a blackboard.

"Well yeah," said Harry, rolling his eyes, surprised at his own daring. "I'd noticed that. What do you – what do you want?"

"A challenge!" said the Selkie hungrily, and Harry was suddenly reminded of Sir Cadogan, one of the paintings at Hogwarts.

"Oh…?" he said, uncertain quite where this was leading to. "Right…"

Ron was now on his feet, and looking over Harry's shoulder at the Selkie.

"What kind of challenge?" he asked.

"A fight," replied the Selkie, and it grinned. This was possibly one of the nastier things Harry had seen before: the Selkie's mouth was full of long, yellow fangs, and its breath smelt of decaying fish. He winced, and took a step back. Around him, his other friends were regaining their consciousness.

"I want…" repeated the Selkie, apparently enjoying their confusion, "… a fight." He grinned, again. "Underwater," he added.

Harry looked at the resigned faces of everyone else, and had to admit that there was no other way they could cross the stream without first eliminating this strange creature in front of them.

"If only we had some gillyweed," sighed Sirius. "Well, there's nothing we can do – I'll have to transform, and – "

"No!" shouted Ron suddenly. "Wait! I've got it…" He fumbled in his pockets, as the others watched on in fascination, and then produced a pack of chewing gum triumphantly.

"Ron – " said Lupin, starting forwards, and looking worried.

"Chewing gum…?" said Hermione, staring at Ron as though suddenly unsure of his sanity.

"No!" said Ron. "Hubble gum. Remember, Harry – I told you about it in my owl. It makes a bubble round your head – go on! Go!" And, before anyone could stop him, he'd shoved the whole lot into his mouth and was blowing with all his might.

"Ron – no!" shouted Hermione. She stared around her helplessly. "Do something!" she screamed. A huge, bulbous sphere was growing around Ron's head like a three-dimensional halo. Harry sprung forwards, but the Selkie was quicker.

"Do you accept my challenge?" it asked Ron. Ron, who couldn't make his voice heard through the bubble, nodded. The Selkie grinned maniacally, and began to revolve again – this time, though, taking Ron with it. The water sprayed the others, bursting out at them in huge waves, but Harry ignored it and tried to tug Ron away from the Selkie's grip. Suddenly there was a burning pain searing down his right forearm. The Selkie's teeth were imbedded in it. He heard someone scream, and with a dull shock realised that it had been him.

"Harry! Get out – that can be lethal!" came Sirius's voice.

"What about Ron?" Harry could hear himself say. He was becoming detached, separated… he knew he was losing his conscious, fast. He caught another glimpse of his best friend as the whirlpool continued, dragging him down with the Selkie into the depths of the innocent-looking stream. Someone caught hold of him, and made a grab for Ron as well. But all of a sudden – there was nothing. The stream was back to normal, and there they all stood – all except for Ron. Harry blinked.

"Ron!" he shouted, finding his voice again. "Ron! Ron, no!"

"Remus!" cried Sirius. "There's a hut up here – look! Quick – bring Harry."

Harry tried to tear away from Lupin in an attempt to rush after his friend, kicking and striking out with all his force. Ron couldn't be dead… he couldn't…

"Harry we can't. It's not safe. I'll – I'll go and look for him in a minute – we have to get to that hut now." Harry couldn't fathom the sudden degree of urgency in his voice before he looked down at his right arm. It was swollen to twice its normal size, where the Selkie had bitten it, and turning white.

"Ron," he whispered, catching sight of Hermione's ashen face. She looked too stunned even to cry.

He barely noticed the horrible howling noise that started again: he heard Snape say, as if through a mist to Lupin – "I'll take Potter. Granger – you come with me. Go and look for the Weasley boy." And Harry was dragged off. The last thing he saw was Sirius and Snape standing over him looking desperately worried, and then everything went black.