As Mark, Naomi and Ellie work together to make sure Isaiah has the best birthday ever, complicated feelings arise. Claire starts to form a bond with Matthew and continues down a path of no return by taking her research to a whole new level.

Mark goes on a date with Naomi, but Eleanor realizes his motives might not be as sincere as they seem. Naomi and her partner, Ben, close in on their suspect, Claire, who has found a terrifying new way to advance her research.