And then the heart changed. 
Spencer let out a gasp - loud and deep - the life returning to him as the blood began to flow again, the venom moving through his veins, setting him on fire for as the blood pumped through his heart, the venom raced through his veins, through his nerves, into the cells, spreading like a cancer, spoiling everything it touched. And as the venom infected him, the moonlight twisted his DNA.
Remus forced the wolf's jaw to release, forced himself to back away, blood dripping from the fur around his jaw, splashing over his feet and the ground beneath him, tangy and horrible in his mouth, between his teeth, in his throat despite how he tried to expel it from his mouth.
He heard the bones cracking, though he kept his face turned away. The gasping and screaming, the begging, the calling his name...
"Remus! Remus what is happening? Please! H-help m-me, R-R- Re--mmuuh-uuuuuhh---"
And the howl that broke in, tore through the night.
The howl might've been a higher volume than the screaming, but Remus would always remember the last few moments of begging as being far louder.
And then the snarling growl, the anger that flooded the room, the tension, hatred...
Remus stared up at the enchanted ceiling, at the trees tops silhouetted against the moon.
Calm down, Remus commanded.
The growling fit and the hatred continued, he could feel the other wolf coming closer, hunting him, could hear the ferocity and blood thirst in the grunts and growls... in the simplicity of the thoughts being flung toward him, uncontrolled, the wolf's violence harsh, cruel, and insatiable.
Remus turned around, baring his own teeth at the wolf he had created. His command was stern: I am your Alpha, I have created you, and you will calm down.
But the new wolf was ready to challenge, and Remus felt his stomach twist.
This is it, he thought, This will define the rest of my life, this fight. I can feel it.
And the new wolf lunged.
Rage makes bodies stronger - be they human or beast - and all of the rage of a newly turned wolf launched into Remus's side, sending him smashing to the floor. He let out a loud wolfish cry, and the new wolf pounced a second time, even as Remus struggled up, dizzy from the blow. Vertigo spun his vision so that everything seemed to be swirling and he rolled just before the new wolf landed on the spot hard enough it would like have crushed his ribs. 
He should have had Prongs come, it suddenly occurred to him. Prongs was big enough and his antlers gave him the ability to block lunges - and Remus realized he'd been foolish to do this alone. Sure, Sirius's dog form wouldn't have been safe here but Prongs... 
The new wolf rebounded quickly and was back again - slashing and nipping, his teeth ripping at Remus's ear. Blood spurted forth and it occurred to Remus that he needed to fight back. He had to - and he had to win - or he would lose the status of Alpha and caring for Spencer moving forward would be near to impossible. He snapped and caught flesh of the new wolf's foreleg and the tang of blood hit his tongue and he was reminded of the bite and his inner human wanted to throw up.
The wolfsbane - a blessing - was quickly becoming a curse.
The new wolf tore at Remus's shoulder, at his hip, at his side... slashing claws and flashing teeth... and Remus slashed back, though carefully, trying desperately to leave as few scars as he possibly could, nipping rather than biting, trying not to break skin or tear sinew.
The moon watched over the unending battle below, silent and unforgiving, as the wolves lunged and snapped and rolled and ran through the trees. And by the time the moon began its descent into the horizon, the ground was spattered with blood.
Sirius wasted no time. The moment the sun had overtaken the night, he was running the length of the tunnel to the Howling House, Lily and James on his heels as Peter and Dora were upstairs, preparing bandages and hot water and blankets. The love magic's strains felt ominous and dark.
Sirius burst through the door into the enchanted forest and looked around wildly until he spotted the blood on the ground. He let out a cry and ran, following the splattering until he found the boys, laying on the dirt in the middle of a copse of trees, spread out on their backs.
Remus's eyes were open, his breath shaking. Spencer was unconscious. Sirius and Lily converged on Remus and James went for Spencer. "Oh my stars, Remus," Lily gasped, seeing the damages.
Remus looked up at her. He could feel blood dried around his mouth and down his chin, could feel it oozing from broken bits of himself, trailing in rivulets over his biceps and chest, on his neck and in his hair. He felt heavy chested like the world was resting on him and he started to sob at the sight of his friends.
"What have I done? What have I done?"
"Are you alright?" Sirius asked, his hands scanning his husbands's body, terrified. 
"His ribs," Lily said nervously.
James called over, "I'm going to move Spencer upstairs and I'll come back for you Rey."
Sirius clutched Remus's hand.
"What have I done?" Remus sobbed, barely hearing the things going on around him. He looked up into Sirius's eyes, "I've bitten. I've bitten!"
"You saved Spencer's life," Lily said.
"It should cost me my own," Remus cried, tears streaming.
Sirius clutched Remus to him but a cry of great pain came up from him and Sirius had to lower him back down. "What's he done to my Moony?" Sirius said gently, his fingers pushing back the curls that were plastered to Remus's head by sweat.
"Not as much as what I deserve," Remus answered.
"You're a hero, Remus," Lily said.
"I'm a killer," Remus replied.
"You're not," Sirius said firmly, "You've saved him from dying, my love."
But Remus could still taste the blood.
And it terrified him.
How would he explain this to Spencer? 
Had this been how Greyback had started? He wondered. Just one to save a life? He thought suddenly of Ned saying that's what Greyback had done for him and Remus felt as though he'd turned to ice. 
James was back then, and Remus felt his friend lift him up, the pain in his chest escalating, though he was unsure if was emotional or physical pain he felt more.
"Here we go, Moony," James said comfortingly as he held Remus to his chest. "It's going to be alright, I swear it."
"You swear it?" Remus rasped.
"I do," James answered.
Remus looked up at James's face for the last few moments before he blacked out - and almost believed him.