Captain America is not the man he used to be. Back in May, it was revealed Steve Rogers has a past connection to Hydra and is loyal to the terrorist organization. This shocked and outraged many readers since Captain America was always a hero with big ideals. How and why Cap was secretly part the group he often fought was soon explained: a cosmic cube had gained sentience in the form of a little girl calling herself Kobik. She became close to Red Skull and rewrote Rogers' past and memories to make him the Skull's greatest soldier.
Captain America still appears to be the same person he was before. The difference is he now has a dark side underneath the surface. Red Skull ordered Cap to kill Dr. Erik Selvig, the cosmic cube expert who helped raise Kobik. While it appeared Rogers followed through with his orders, it turns out he may still have some free will. The question remains: How far will Captain America go to fight his mind control? There will be spoilers for Captain America #4 below.
Because Cap didn't kill Dr. Selvig, it appears there can still be hope for the hero. Perhaps he is able to fight Kobik's reprogramming and Red Skull's orders. Captain America normally doesn't kill his opponents even though he was a soldier in the war. He believes in instilling justice for all but simply is not the type that would kill in cold blood.
Selvig was surprised Cap went against the Supreme Leader's orders. Rogers believes he and Selvig can restore the glory of Hydra without the Red Skull. To kick things off, he brought the doctor to a lab belonging to the villain, Red Ghost. When Rogers arrived, Red Ghost ordered his three super-powered apes to attack. They did not pose too much of a threat for the super-soldier.
In a brutal manner, Rogers quickly put an end to the apes. This was a shock to Red Ghost, who decided his best course of action was to flee through a wall using his phantom powers while his apes continued to protect him. Cap stopped Red Ghost's escape which resulted in an arm and leg being severed.
Rogers then used Red Ghost to access the lab's computer system. Accepting defeat, Red Ghost tells Cap he should just leave him now that he has the information he wanted from his files. Rogers didn't see it this way and determined he also needed Red Ghost's silence.
We may not see Red Ghost's final fate on the page, but it's pretty clear what happens next. Killing Red Ghost is crossing a line for Captain America. He may be under the cosmic cube's control, but the fact that he's fighting the programing suggests there may still be some of his old personality locked away. Then again, killing the apes and Red Ghost is extremely out of character for the Avenger.
Regardless of how this story ends, if Captain America has his past returned to what it should be by Kobik, he still has crossed a line. There will be repercussions to deal with. If he continues down this path, returning to his former glory will become more difficult.