[Jason Abbadon]

I just read the issue explaining exactly what I figured- that Bucky was indeed beaten and stabbed by Sin but his pulse was still barely hanging on so Fury and Natasha had him medivaced to a secret base where they shot Bucky up with the world's last dose of Infinity Formula.
Fury's body makes it naturally for him (after so long taking it) but they did ot know if it would save Bucky's life or what...so they swapped an LMD (with matching wounds) and faked the Avengers and Steve out about his death.
They decided not to tell Steve because his head needed to be in the game during the whole Fear Itself thing and they did not know if Bucky would survive anyway- he did not pull through till days after it all ended.

Still, Steve was pissed enough to beat on ol' Nick some (Nick not fighting back) untill Bucky himself showed up to talk to Steve.

real good damn issue with solid art.