'Agents of SHIELD': SPOILER Makes a Surprise Return

The 100th episode of Marvel's Agents of SHIELD featured the surprise return of a key character from early in the show's history.

SPOILERS for Marvel's Agents of SHIELD, "The Real Deal," follow.

In tonight's Marvel's Agents of SHIELD, the explosion of that Kree beacon that concluded last week's episode is revealed to have destroyed all three of the Kree monoliths that were stored in the basement of the Lighthouse bunker. Their destruction created a tear in spacetime that opened up a gateway to a dimension of fear. That fear was leaking through the tear and giving a physical manifestation to the deepest fears of the SHIELD team.

In order to seal the breach, Phil Coulson took a gravitonium grenade into the basement. He knew that his greatest fears would be waiting there for him, but he didn't expect to see Mike Peterson.

Peterson was introduced in the first season of Agents of SHIELD. He became involved with the nefarious Project Centipede and believed he was on track to become a SHIELD agent. Instead, the Hydra sleeper agent John Garrett got a hold of him and turned him into the cyborg known as Deathlok.

However, the Mike Peterson waiting in the basement was fully human, at least in appearance. Peterson admitted that he was a figment of Coulson's own mind, but explained that was because Coulson was dying. Everything that had occurred in the past several years was actually the random synapses in Coulson's brain firing as a medical team tried desperately to bring him back from the brink of death after being stabbed in the heart by Loki.

Peterson seemed to be getting to Coulson and nearly convinced him to walk into the light, but Coulson fought the temptation and refused to believe that what he'd lived through wasn't real. Peterson became violent and attacked Coulson, but that's when the real Deathlok showed up.

Deke went out into the world to get a message to Deathlok, and he and the remaining agents of SHIELD in the field made their way to the Lighthouse. Deathlok arrived just in time to fight off the other version of himself, Lash, two Vrellnexians, and Hive.

Later, Coulson explained that Deathlok has been operating solo, but went out of his way to help some of the SHIELD agents who went on the run after the LMD of Quake tried to kill Glenn Talbot. He won't be sticking around, but it was a good thing he arrived when he did.

Marvel's Agents of SHIELD airs Fridays at 9 pm ET on ABC.