He told SFX that security officer Cromwell is revealed as "quite a dark character" in the eight-part BBC drama.
"He carries around with him a very dark past," explained Mays. "As the series unfolds, [you discover that] he's carrying around with him a very dark and quite disturbing secret."
The former Ashes to Ashes star explained that the series will serve as "a story of redemption" for Cromwell.
"The best thing about playing him was just how layered he was," he explained. "More than any other character in the show, it's his second chance. Whereas other characters in the show are connected still to Earth and are longing for relatives to come to the planet."
Series creator creator Ben Richards previously revealed that he is keen to make a second series of the sci-fi drama.
Outcasts begins this Monday at 9pm on BBC One.