Having received an ominous threat from her old boss, Amunet (guest star Katee Sackhoff), Caitlin (Danielle Panabaker) fears that her past time as Killer Frost may be back to haunt her. Felicity (guest star Emily Bett Rickards) comes to Central City to help the girls celebrate Iris’s (Candice Patton) bachelorette party, while Cisco (Carlos Valdes), Joe (Jesse L. Martin) and the guys take Barry out for a night on the town.