Red flag number three. This is one of the most obvious red flags in the history of all red flags. Harry Potter and Albus Dumbledore went to find a horcrux of Tom Riddle...Harry Potter, a wizard who hadn't even finished school...and Albus Dumbledore, a wizard who is old as dirt...going to a cave where Tom Riddle probably tortured other orphans...to get a Horcrux which is really dark magic...the Horcrux of arguably one of the strongest dark wizards of all time...hmmm...is this really the smartest decision? Who knows? Definitely not Harry.
At the time Harry had thought about it as one of the greatest light wizards who had defeated Gellert Grindelwald with Harry Potter, the chosen light savior who was destined to defeat Lord Voldemore, but honestly, Harry hadn't even finished school let alone knew enough magic to get around the traps that Lord Voldemort most likely had around his soul piece. Either way, the duo were probably not enough to find and destroy a horcrux. If only he had thought about it for a bit longer and a bit more thorough.
They headed out together with Dumbledore apparating them to a cliffside, how Dumbeldore managed to apparate from Hogwarts was anyone's guess because according to Hogwarts: A History it was supposed to be impossible. When they reached the front of the cave, Harry had to question what Riddle was even doing there to begin with. The inside of the cave was dark, dreary, and grossly moist. It screamed of warnings but they went inside anyway. They reached the back of the cave and Dumbledore looked at the wall closely.
"Very clever. It seems that Riddle wanted to weaken his enemies before they even entered the chamber. It requires a blood sacrifice that will weaken the one who enters". Dumbledore pulled out a knife and seeing Harry's alarm he reassured him. "Don't worry, this won't affect me that much, it was made for weaker wizards".
The blood that oozed from the wound was not reassuring even when Dumbledore healed it and moved through the opening that was exposed after smearing his hand against the rough edges of the wall. Inside was pitch black and it sounded like there was water inside from the sounds of slouching. Dumbledore reached for his wand and cast a modified lumos. The ball of light expanded from the tip of his wand and then was released to the center of the room. It was a much larger and darker cavern with a large body of water in the middle, just as Harry had suspected. In the middle of the cavern, was a mini island with a medium sized column. They stepped in and looked around for a way around the water.
Dumbledore pulled up a chain from the floor and when he pulled, it revealed a medium sized boat. The boat was nothing spectacular but a normal wooden boat, but Harry was certain that there had to be enchantments on it that would be particularly unhelpful. "It is enchanted to only allow one wizard on it," Dumbledore revealed.
"Shouldn't we be worried?" Harry thought that Dumbledore looked way too relaxed considering the situation that they found themselves in.
"Not at all, the enchantments classify a wizard as someone who has reached their magical majority, which fortunately does not include you. One of Riddle's biggest weaknesses was he always thought that he was the smartest wizard and few people are threats in his eyes."
They got in the boat together and the boat seemed to paddle itself to the island. As they moved through the water, Harry peered over the side of the boat into the water and felt unnerved by the darkness. "Don't lean over too far Harry, I suspect that you would not appreciate the results" Dumbledore peered with his all knowing gaze over the tops of his glasses.
The boat gently bounced off of the island and they got out. In the middle, the column had a bowl like structure filled with an unknown liquid. Beneath the liquid was a necklace with a green gem with the letter S. "Slytherin's locket. Thought to be lost to time but it seems to be right in front of our eyes," Dumbledore's hand tried to reach in to grab it but it seemed to bounce right off of the fluid like a solid barrier. Despite how many different spells Dumbledore used they all seemed to fail against the impenetrable barrier. Using a transfigured goblet, they discovered that the liquid can be drained but not poured out of the cup.
"Just as I thought, Tom would not allow for any person to leave without drinking the potion which would further weaken them," he sighed and turned towards Harry, "you must promise me that no matter what happens when I drink this that you will not stop giving it to me."
Harry's chest seemed to tighten with the words and he felt like he couldn't breathe. Why did Dumbledore seem to think that he would be forced to drink the potion? What kind of potion weakened someone and if Riddle had picked it out then surely it would be a poor decision to drink it?
"Can't we transfigure something else to drink it? Why do you have to drink it?" Harry knew that he was grasping at straws because why would any idea of his work where Dumbledore had failed.
"Unfortunately, when I bled upon the cave wall when entering I consented to a contract. I cannot get the locket without drinking the potion. I had felt the contract seal when I bled upon the wall but I was hoping that Riddle had left a loophole, it seems that I am the one who had underestimated him. My boy, if there was another way then I would never ask this of you, but for the greater good I need you to do this or all that we have done up to this point will be wasted."
Harry nodded, he figured that there must have been a reason against his logic but he couldn't help but briefly hoped that he had found a solution. Dumbledore, with the help of Harry, drank the potion but with cup after cup, Dumbledore began to fall. Not literally, but his will had started to fail him. He begged and with a desperation that Harry had never seen he tried to resist Harry from forcing him to drink. Harry was horrified. This was one of the greatest wizards of all time and Harry was forcing him to drink an unknown poison.
Finally, his torture was over. Who suffered the most was hard to tell. Dumbledore was lying by the side of the basin with a weariness beyond his years and was asking dryly for water. Harry, desperate to end Dumbledore's suffering, tried to cast aguamenti but when that failed he went for the closest water source, the water around the island.
Lowering the cup to the surface of the water, Harry realized that he fucked up. His mind flashed to Dumbledore's warning about the dangers of the water but it was too late. A grotesque hand reached out of the water and grabbed him with an unworldly strength. Harry, bent too close to the edge, was easily dragged in and began to flail to get away. His desperate actions were too little, too late. Underwater, he tried fighting the unknown creature with little success. He lost his glasses in the process and he vaguely saw them seeking into the dark abyss. From the darkness he finally got to see his opponents fully.
Bodies. Not dead. Not alive. Rotting though. Their eyes although unseeing and opaque managed to see where he was and three of them pulled him close to their gaping mouths. There were many more in the distance, at least a few score, but they were still dragging their bodies through the thick water. Briefly in the back of his mind a voice answered his unspoken question regarding the horrifying creatures. Inferi, animated corpses that have no will of their own, very lethal and very violent. Harry struggled and his lungs burned for air. He finally managed to grab his wand and cast a repelling spell, one of the few that he managed to cast wordlessly. The charm didn't work fully but it was enough for him to drag himself towards the surface and finally get a huge gulpful of air.
Harry quickly dragged his body onto the island but the inferi were not discouraged. They were awake and nothing could prevent them from getting their prey. The orders of their twisted master were clear: kill everyone.