Author's Notes: Firstly, this is indeed a Harry Potter and Half Life: Opposing Force crossover, but it's been written seriously, hence why neither of the genres is humour. Secondly, I own none of the concepts, characters, or books I refer to, and this goes for ALL the chapters. Thirdly, if you enjoy this fic, be sure to check out its counterpart in the Games: Half Life section of this site. It's called HalfLife: Opposing Force: The Alternate Reality. It is an identical story to this, but written from Corporal Shepherd's point of view, offering a completely different narrative and answering some of the questions this fic leaves open. Fourthly, whether you like the story or not, review it for God's sake! And review my other one as well, because nobody's reviewing it!

Harry was daydreaming about being a ceiling fan. This was what today's History of Magic lesson had reduced him to, imagining what it would be like to be different inanimate objects. Usually Professor Binn's lectures involved things which had the potential to be interesting if it was imagined in one's head in the right kind of light, e.g. epic battles, but today the dead fogie was dribbling on about the development of magic wands, and their predecessors, magic staves. Harry had gone into such an advanced state of lethargy he felt as though all his muscles had gone into entropy. With all the speed he could muster, he slowly craned his neck left. Hermione was rapt with attention, scribbling furious notes down onto her parchment. The look of concentration on her face was unbelievable amongst the ocean of boredom washing around the room. Harry slowly turned his head right. Ron appeared to be performing palmistry on himself, writing down his findings on parchment with such a lack of speed it was plain he didn't even vaguely care about the findings. Harry had already gone through all his usual standby things to think about when he was bored, wondering what Voldemort's next move would be, fantasising about Cho, imagining he was a ninja etc. but all of these topics were spent. So in his head he was composing a haiku about the life of a ceiling fan. The room was a time vacuum, sucking out all the time so its denizens were forced to endure purgatory for days on end when in reality the lesson was only a couple of hours long.
Suddenly the bell rang. Life reawakened around the room; suddenly Harry could hear the birds outside, and the comparatively pathetic British summer sun was warming him from through the window. Simultaneously all of Harry's muscles worked themselves out of entropy, and Harry gingerly stood up. He walked out of the room woodenly.
"That was as bad as a lesson can get without Snape or Umbridge being involved." Harry opined to Ron and Hermione once they had left the room.
"I think it's a disgrace that so few people listen to Professor Binns," she snapped back. "That lesson was very interesting and well put together."
Ron sighed. "Hermione, History of Magic doesn't have the same effect on other people as it does for you," he explained. "For example, when I'm in a History of Magic lesson my brain slows down slower than a troll's."
"No change then." muttered Hermione. Ron didn't catch it.
"And for me," Harry supported, "it's a kind of reverse-Yoga. All my joints seize up and I just want to die."
"Oh, stop being so dramatic, it's just a lesson!" Hermione replied heatedly.
"I wasn't being dramatic, I was being honest." Harry defended. "Listen." He stopped walking. He bent his neck to each side, resulting in several sharp cracks. He then straightened out his elbows one at a time, inciting one more crack each, and proceeded to crack every single movable joint in his body. His grand finale, after cracking all three joints in every one of his fingers, was placing his hand behind his back and leaning back on it sharply, with half-a-dozen high-pitched cricks echoing off the stone walls. Several onlookers broke into mock applause, and Harry sank into a mock bow. He continued walking. "I don't see how History of Magic doesn't qualify as a health hazard if it does that to me."
Hermione didn't dignify this argument with a response.
It was now lunchtime, so the majority of the students were making their way towards the Hall. Harry, Ron and Hermione took a slight detour to enjoy the spectacular view out of a curving, third-floor window of the Hogwarts grounds and lake. The sun was high in the sky, throwing the dark undersides of the leaves of the nearby tree into sharp contrast with the glaringly bright tops. It was an absolutely gorgeous day. Which would soon be ruined by external influences.
"Hey!" Ron exclaimed. "What's going on there?"
Centaurs were emerging from the Forbidden Forest in a state of high alert. They were being led by Bane, who was shouting orders as he and his group stampeded towards the castle, bows and spears held high.
"What on earth are they doing?" Harry demanded. "What could have made centaurs so angry they're going to come down to the castle?"
Hermione grabbed his arm and choked out a suspicion. "Do you suppose - Grawp? -"
"No." Harry said instantly. "Hagrid had him under better control than this." But his voice was doubtful.
Then, adding to their confusion, other magical beasts started pouring out of the boundaries of the Forbidden Forest, the likes of which they'd only seen before in textbooks. Beasts of every description, all charging side by side in synchronicity, including beasts who were definitely mortal enemies of each other and should be at each other's throats.
"Grawp couldn't do all this." Ron stated slowly.
"What on earth is going on?" Hermione wondered, fearful.
"You'll never know, Mudblood." Draco Malfoy appeared. Crabbe and Goyle followed, as always. His vile smirk twisted his face into something subhuman.
"I've told you not to call her that - "Ron seethed, starting to draw his wand, but stopping when he saw Malfoy's wand was already in his hand.
Harry stared at Malfoy. "Do you know something about what's happening?" Harry asked quietly.
Malfoy laughed maniacally. "It's a purification." He drew breath for an incantation, made the beginnings of a wand movement.
However Harry had trained in Dumbledore's Army, and after such extensive practice could draw faster than Billy the Kid. His wand appeared in his hand as though by magic and he screamed out the five syllables of "EXPELLIARMUS!" before Malfoy could even start to talk. Malfoy was blasted backwards and hit his head on the fist of a suit of armour, his wand flying the other direction into Harry's outstretched left hand. Ron and Hermione had their wands out even before Crabbe's and Goyle's snarling expressions had fully changed into looks of fear. Ron and Hermione waited, unwilling to hex unarmed people, so Crabbe and Goyle fled. Harry walked over to Malfoy and checked him.
"He's out cold." he said aloud for Ron and Hermione's benefit. He plucked the Inquisitorial Squad badge from Malfoy's robes, examined it, and threw it out the open window. Then he snapped Malfoy's wand in half, snapped it into quarters, and dropped it onto Malfoy's unconscious form. "You don't deserve to be in Hogwarts." he murmured half-aloud.
"This is bad." Ron announced, scared. Harry looked out the window. The creatures from the Forest were swarming around the school grounds! Then, the cloud of magical creatures turned towards Hogwarts School itself and moved towards it purposefully! There was a nuzzling third-year couple sitting in the shade of one of the trees. One of them, the boy, stood up and shouted. One of the centaurs loosed off an arrow at the kid in passing, sticking him full in the chest. Hermione screamed. Two other centaurs shot him as well, and another one shot the girl in the head. Harry felt numb with the inhumanity of it. Homicidal, remorseless creatures were teaming up and invading Hogwarts with the intention of killing the students! It was unthinkable.
"Harry?" Hermione's broken voice pleaded. Harry snapped his gaze from the two corpses by the tree. Both Ron and Hermione were looking to him. Asking for help and advice without speaking. The bloody idiots! Did they really think he had the foggiest of ideas what the hell was going on, or what they should do? But suddenly, he knew what to do; interrogate Malfoy. Assuming he hadn't been full of it earlier when talking about a purification, he knew something. Harry turned. Malfoy was gone. He had left the pieces of his wand, but he had definitely legged it. Obviously he was not as out-cold as he had appeared to be.
"Damn!" Harry shouted, and kicked the suit of armour. The shout and the clang echoed down the long hallway. A thousand accusing voices damned him for letting that toerag Malfoy get away. He considered their options. "Okay, find Dumbledore." Harry decided. When in doubt, find Dumbledore.