Everything is canon up to the end of the fourth book. Might turn this into a Harry Luna fic, we'll see.
Disclaimer: I don't own anything, I'm just borrowing characters and settings and saying my opinion on what should have happened
*The end of the Third Task of the triwizard tournament right after the sphinx clue*
Harry saw Cedric running ahead of him, after all this hard work Harry realized Cedric had beaten him again, just like their last quidditch match. All Harry felt was disappointment in himself. Then Harry noticed something moving towards Cedric, on a course to cut him off. Just in the nick of time Harry shouted "Cedric! To your left!". Cedric looked left just in time to leap forward out of the way of the thing that was coming. It was a giant spider. That riddle Harry just solved must have been a clue for the next obstacle. Cedric looked around, the spider was bearing down on him, coming closer, pinching its pincers together. Harry had to act, he couldn't let Cedric get eaten in front of him. "Stupefy!" Harry shouted. For all the good his spell did he might as well have thrown a stone at the spider. Feeling the spell, the spider scuttled around to face Harry. Harry started throwing every spell that came to mind at the spider before it could get to him. "Stupefy! Impedimenta! Expelliarmus!" but these had almost no effect on the giant spider. The spider bent low to grab Harry but as its pinchers came ever closer to Harry's body a thought came to him "Incendio!" he shouted. The spell hit the spider's hairy face and ignited it, causing the giant spider to flee, freeing the path to the triwizard cup. Cedric came out of a sort of daze, realizing the danger was gone. "Harry, I'm sorry I couldn't help! Using fire was a brilliant idea. You deserve the cup, Harry, not me…" Cedric mumbled as Harry got close enough to see if he was alright. "Don't be thick" said Harry "you got here first, just take the cup". Cedric replied, "You helped me with the dragons! And you've saved my neck in here, that's twice now. You take it, go on." Harry looked over at the cup, tempted to go grab it and take all the glory for himself. But no, he couldn't do that. "Together." Harry said. "You sure?" replied Cedric, sounding surprised. "Yes, on three… one… two… three!" They both grabbed onto the cup and felt the familiar jerk on the back of their necks that meant that they had grabbed a portkey.
Harry and Cedric found themselves in a graveyard, it was dark, cold, and clammy. "Wands out?" Said Cedric. "Yes, good idea." Harry replied. Then a high cold voice rang out, "Kill the spare, Wormtail!" then Harry's quidditch reflexes kicked in. He saw a green flash of light and he tackled Cedric to the ground, the cup was only feet away. Harry sent two stunners back and felt relief flood over him as he heard wormtail fall over. Cedric was blown away by what just happened. "Bloody hell" murmured Cedric. Harry could only think to say "yeahh…." "Mind getting off of me? I think we're safe now, thank you Harry" Cedric asked. Harry hastily stood up. Harry wondered out loud, "How in the hell are we getting back to Hogwarts? Where can we even be?" "I dunno, maybe try the cup again, see if it's still a portkey?" Cedric asked. "Good thinking Cedric, let's take it on three again?" "Yeah, let's go, one... Two… three!" They were returned to the Hogwarts grounds, each holding one handle of the Triwizard Cup, looking bloody, battle worn, and victorious. They had won the Triwizard tournament, tied for it, a Hogwarts victory. The crowd watching the final task went nuts. There was screaming and cheering from the Hogwarts crowd, and booing from the Durmstrang group. Dumbledore's voice boomed out as if he were speaking through a megaphone "It appears we have two Triwizard champions! How extraordinary! The Awards Ceremony Will be directly following lunch tomorrow. For now everyone shall return to the castle or their quarters. Thank you all for coming to see this extraordinary end to a once-in-a-lifetime event. Just a few more words and you'll all be free to go, so here they are, tortoise, yonder, ailment, and smarm. Good night to you all." Only Dumbledore seemed to notice that something was very wrong by the looks on Harry and Cedric's faces. "Come with me, to my office, the both of you." Said Dumbledore in an undertone.
Harry, Cedric, and Dumbledore arrived in the headmaster's office about twenty minutes later. "What seems to be troubling the both of you?" Dumbledore asked. Harry and Cedric told the tale of everything that had happened since the beginning of the task up until their return from the graveyard. Dumbledore looked furious. He said "Stay here Harry, Cedric" and Dumbledore grabbed Fawkes' tail and disappeared in a ball of fire.