Walker's night at home gets interrupted by a phone call. His friend Sam Bower has just been admitted to a hospital with a heart attack. Walker thinks he has been dosed with a radioactive substance by the Russians. Sam is unconscious but keeps mumbling about a mission in Russia. Reid's trial has been pushed back six weeks. His lawyer Fiona points out that the six weeks will give them more time to find the woman he remembered. The BAU finds two more cases like Sam's, then a fourth gets attacked. The unsub is mimicking a Russian espionage technique. Walker keeps flashing back to a mission with Sam in Russia, 2013. A fifth victim, Alex McLean, gets poisoned, from something he ate. There's radioactive material at his house. His wife Sarah is the unsub. Reid's mother comes to visit him in prison, although she didn't know he was in there for a murder charge. They surround Sarah, who takes a hostage, then Rossi shoots her. Sam asks to see his son Zach. Sam dies just after Zach arrives. Diana blames herself for Reid's incarceration, and worries that she will forget him before he gets freed. Reid recognizes Diana's new nurse as Lindsay Vaughan, an unsub from Reid's past.