S4, E18: Supergirl and Lena head to Stryker's Island to search for clues on how to defeat Lex. At the prison, Supergirl tries to befriend a nosy prisoner, Steve (guest star WILLIE GARSON), who may have insight into what Lex was doing, but he and all of the prisoners regard her as a traitor to the country and refuse to talk to her. Lena realizes Lex left behind clues for her and deciphering them could be the key to his whereabouts. Meanwhile, Kelly encourages James to talk to someone about his PTSD, and Alex faces off against Ben Lockwood after he storms the DEO and acquires some powerful weapons to hunt Supergirl.