Starts at the end of PoA. Wormtail didn't get away and Harry is given the life his family wanted
With that in mind they started making a quick plan to return to the castle. Harry's mind was already made up, he now had a godfather, some one who was a true link to his parents and he was not going to leave things to chance. With that though in mind he started to voice his concerns, “Professor Lupin, did you take your potion today? If not, you will need to remain here because it is just about night fall and your affection could cause problems right now”. “Shit! I...I did not take it, with all that was happening, I completely forgot about it. How could I be so stupid?” Hermione quickly cut him off by saying, “Professor, you are far from stupid, with all that’s been happening today, with the thought of seeing one of you best friend for the first time in all these years, anyone would forget. However, Harry is right you will need to say here.”
So with that said Harry quickly started giving out directions for everyone. He told his godfather to stun wormtail and bind him in rope that had the nessacrary jinxes on them to prevent Pettigrew from transforming or apparating. He them walked over to where Snape was still laying knocked out from his earlier disarming spell. Harry gave Ron instructions to bind and levitate there potions professor. Ron started to say, “Mate, my leg”, but Harry was already tapping his leg with his wand and muttering a spell, after which his bones healed and was pulled up by his hand. Ron and Hermione both just looked at Harry as if they had a million questions. Harry cut off the questions with a wave of his hand and told them he would answers all questions later but for now just do what I ask so we can all get out of here. “Now, Ron you go on ahead, take Snape with you and get to Dumbledore as soon as you can. We will be following you with the traitor. Do not tell him anything except that we are on our way up and could use his help.” Ron gave a nod of his head and left through the trap door with Snape levitating behind him.
Harry then turned to address the others, “Sirius it would be best for you to turn back into your dog form and follow Hermione and myself back to the school. Hermione I want you to levitate Pettigrew and I will follow you with my wand on him just in case he comes to, if he so much as blinks his eye, I will not hesitate to take a bigger piece than just a finger. Professor, thanks for all of your help today, without you here to disarm me I would have made the biggest mistake of my life.” With a look of great pride Lupin walked over and placed a hand on Harry’s shoulder and looked him square in the eye, “Harry, your mother and father would be so proud of the man you are becoming. I’m just sorry I can’t be of more help right now but I will see you and Sirius in the morning, now you all should be going, the sun is about to set and things could become more difficult. With one last look at everyone he gave a nod to Hermione. She then looked at the man who stole her best friend family, pointed her wand “locomotor Pettigrew” and his body rose to about three feet off the floor. Harry then gave Sirius an expectant look with raised eye brows and a small smile. His gave a slight chuckle and transformed back into his huge black dog. Harry gave a nod of his head, drew his wand and pointed it at wormtails head. He followed Hermione out of the trapdoor, through the tunnel and back out the opening at the base of the womping willow.
As the group started making there way back the castle, Harry had a smile on his face that could light up the darkest of rooms. Hermione looked over her shoulder and with a small smile on her face she thought to herself that Harry is finally going to get the kind of life that he deserves. However, that thought was short lived as the temperature in the air started to drop rather quickly. Hermione then turned around with a horrified look on her face. “Dementors”, whispered Harry. Than the darkness started to press in on them, they could hear small whimpers coming from the large black dog and the air itself started to press in around them. At that moment Harry felt a creeping chill from behind, turning around, not 20 feet away was one of the horrible creators moving toward them. He could already hear the voice of his mother and flashes of green lights in his mind. “Not now” was all Harry could think, his thoughts just moments ago were that he might actually have a life, he might actually be able to get away from his so called family, he might be able to start a life with a family that loved him because he was Harry Potter not some freak. Thinking of Sirius, of his mother, of his father, he pointed his wand at the dementor and using the spell professor Lupin taught him he shouted out “EXPECTO PATRONUM!” Out shot a huge, bright sliver, charged full of love stag. It proceeded to charge down the nearest dementor and continued to scatter the rest of foul beast. After what seemed like hours but was no more than a few seconds the temperature began to rise and the darkness that was pressing down upon them was lifted.
With his wand rose to the sky Headmaster Dumbledore, with long strides, quickly made his way down to the group, “Miss Granger, Mr. Potter are you alright?” “Yes sir,” both kids spoke up. “Harry, what is going on here?” the Headmaster asked while looking at the man who was now laying on the ground still bound and knocked out. “Professor Dumbledore, this is Peter Pettigrew, the man who was my parents secrete keeper, the man who betrayed them to Lord Voldemort and also the man who allowed one of his best friends to rot in Azkaban for twelve long years for a crime he never committed.” With that statement being made Dumbledore just stared down at the heap of man on the ground, “can it be” with his customary twinkle in his eye. He then looked up at Harry than at Hermione, the smile that started small was now fully reaching his eyes. “Miss Granger, Mr. Potter I’ll take the prisoner up to my office and I’ll fire call Madam Bones of the DMLE to get the legal proceedings started. Would the both of you be so kind as to escort are guest to the hospital wing” while looking down at the large dog with a great amount of pride, “I shall alert Madam Pomfrey that he is of no danger at all and has had many difficult years. However after you help our friend to that location, if you both would be so kind as to come to my office, I think we have much to talk about.” “Yes sir” and “yes Headmaster” was stated by both Harry and Hermione respectfully.