When Catherine’s dad gets remarried, the bride-to-be and her bridesmaids try to find the daughter-of-the-groom a date for the wedding. Uncomfortable with being set up, Cat reluctantly admits that she’s seeing somebody and confides to Vincent that she wishes he could be her date. At the wedding reception, Cat learns about a research grant that Evan received to study the mutant DNA cells found at local crime scenes. When she tells Vincent about Evan’s theory of how the cells are changing to become more animal-like and less human, she encounters an unexpected detour that could change the course of their relationship. Meanwhile, Tess and Joe cross the line romantically despite the fact that Joe is a married man.

On the anniversary of her mother's death, Cat asks Gabe to attend her family's annual remembrance of Vanessa, which makes Vincent incredibly jealous. Cat learns some information that makes her think her mom might still be alive and when a sniper shoots the mayor at a public event, Vincent finds evidence that links Gabe to the sniper.

In order to prevent Vincent from further injuries, Cat helps protect Tori when her life is threatened, revealing a new, unexpected mystery. Meanwhile, Vincent's stubborn attempt to intervene leads to life-changing consequences, which causes Gabe and Cat to grow closer.

When Cat is assigned to a new partner by Tess, she begins to suspect that Bob and Carol have re-surfaced to separate her from Vincent and hunt them both down. Meanwhile, a transformed JT discovers that his newfound healing ability comes at a terrible cost.