This is just an outline, a burst of inspiration if you will. I am working on the chapters right now and they will be different then this. You may use the idea that Harry is an Immortal. Thank you.
So it was love that saved Harry on the night on Holloween? Is that really the explanation? Not in this timeline!
Harry survived because of a certain organization obsessed with immortality had used him as a test subject when he was 9 months old. The elixir was pretty good. Harry survived all ways they used on him to die. It an apparent success until a month later that it but the problem? He was still aging. Just after realizing this they were ambushed by Firo and his men. Harry was saved and sent back to Lily and James. Months later Harry died by the killing curse that, with the power of Harry's magic, forced back to Voldemort destroying him. Harry as revived right before the first person walked in. The rest you know if you read the books.
Well right up to around his 13th birthday when his aging process freezes and then during his 5th year when he was unable to do the lines that Umbridge has him do because of his immortality.
Maybe timeline
"This place is a lot different then I thought it would be." Firo was walking down a hall lit up with torches and lined with suits of armor. "Now what hall was Snake talking about? Main Hall? No. First Hall? No, that's even worse... Oh! The Great Hall! That's it! Now what giant doors was he talking about?" Firo turns a corner and stops. "Oh those giant doors."
Near the middle of the hallway was a pair of wooden doors. They reached just below the ceiling and light could be seen coming threw the cracks. Firo was now standing in front of them, hearing chatter of hundreds of people had reassured him that, yes, these were the corrects doors. He was about to open them when yelling quieted the entire hall. All though he couldn't hear the words being spoken he could make out that an argument had occurred. It sounded like an older female trying to lecture a younger male. 'Maybe if I just open the door a little.' He could now hear that voices clearly.
"As I have stated time and time again Mr. Potter," 'Potter?' "Cedric Diggory's death was a tragic acci-"
"It wasn't an accident! I saw what happened. I. Was. There! You government officials just don't want to admit that Voldys back!"
Gasps could heard all around that hall.
"Detention Mr. Potter!" The lady moved and Firo was finally able to see the boy clearly.
"Harold?" Firo wispered
"For what Professor?" Harry spat the word out as if calling the other that very word was venom. "Telling the truth?"
*Smack**Thunk*
Maybe timeline
Firo was caught by Dallas(yes still alive and kicking) and his goons while he was taking care of things in Scotland they were able to somehow sneak Firo into the "run down castle" over Christmas break when everyone, yes including Harry, the headmaster, filch and everyone was out. Firo was imprisoned in the dungeons and was subject to harm both physical and mental. Dallas had taken his right hand and put it somewhere were he cant get to it so Firo can't devour them and get away.
After everyone comes back over break it took only a few days for them to be discovered. Well more like Firo discovers them when he gets out of his cell and runs like hell in only shorts and a tank top into the great hall during dinner. Although, with all the enchantments on the castle he doesn't see them but they see him. He runs into the great hall and looks around searching for his hand. He sees the location and runs towards it. He gets to the container and was only able to loosen it a bit before he was grabbed from behind by Dallas and his goons. Dallas tells(brags) a story about how he had devoured a special person that could do extraordinary things and he wanted to try out something from his memory.
Dallas has two on his goons hold Firo up and then pointing at him as if holding a gun shouts "Avada Kedavra" The green light shoots from his hand and hits Firo right in the head. Firo is dropped to the floor seemingly dead.
"ohhh so that was the killing curse." Dallas walks over to the unmoving Firo and squats down just as Firos hand breaks free of its comfinments and reataches its self.
"Seems your not dead but theirs no pulse or breath." Dallas stands and grins "Lets see if we can restart your heart" he stomps on Firo's chest, hard. Firos gasps as his heart and lungs restart.
This is just an outline, a burst of inspiration if you will. I am working on the chapters right now and they will be different then this. You may use the idea that Harry is an Immortal. Thank you.