Cat finds information in a surprising place -- her ancestor's journal -- that makes her think the only way to stop Gabe is to kill Vincent.

When secrets about Cat’s family are revealed, it will change everything Cat knew about her past. Vincent finds himself staring his demise in the face; while Gabe takes drastic measures get some answers.

Cat and Vincent go on a date out in public in an attempt to be a normal couple, which backfires on them. Meanwhile, Gabe reveals some information that gives Cat hope they can find a cure for Vincent.

After taking their relationship to a new level, Cat and Vincent are forced to deal with reality when someone appears to be the framing the vigilante. Evan finds proof that Cat knows more than she is letting on about the beast. Muirfield and the police are closing in on Vincent and this time there is no escape, so J.T. and Cat come up with an extreme solution. Meanwhile, Tess following a tip, finds something that will forever change her relationship with Cat.

JT thinks Vincent may somehow be involved in Cat's homicide investigation after she mentions a local college fraternity brother was brutally killed. JT examines Vincent to determine the cause of his increasingly frequent blackouts, but when Vincent starts to beast out, JT is forced to tranquilize him. Meanwhile, Evan and his new intern find a strange cut on the victim's ankle, which matches that of a female cadaver left on campus a year earlier. As Evan works to uncover more clues from the crime scene, he is kidnapped. Cat begs Vincent to help find Evan and save his life, yet she doesn’t realize that she’s putting Vincent's life in serious danger.

Cat suspects Muirfield might know Vincent's whereabouts and in spite of her vow to go cold turkey, she is forced to interrupt his romantic cabin getaway with Alex in order to save their lives. Meanwhile, Evan finds a bug in his lab and becomes increasingly suspicious of J.T..

Cat and Vincent are unsure if they can trust Alex (Bridget Regan) with the truth about his past. Evan realizes that Claire (Kelly Overton), the woman he is dating, is hiding things from him. Heather (Nicole Gale Anderson) meets and falls for Joe's younger brother Darius (Christian Keyes), and Vincent tries to win over Cat with romantic gestures for Valentine’s Day.

Evan confesses his love to Cat and admits that he tipped off Muirfield to Vincent’s whereabouts. Meanwhile, Gabe finds evidence that someone in the department is a mole who was working with the vigilante.

Vincent is torn between his new feelings for Cat and his old memories with Alex (Bridget Regan). J.T. learns that Evan is planning to propose a task force to catch the beast and must figure out how to stop him. Meanwhile, Tess investigates the mysterious skydiving death of the wife of a billionaire adventurer, while Cat remains off duty until she recovers from being shot.

After a dinner where Cat introduces Vincent to Heather ends badly, Heather enlists Tess to stage an intervention with Cat. Evan receives an interesting proposition that could change the course of his cross species investigation and at an event to honor Joe, Heather goes missing and Vincent is forced to make a tough decision that saves her life.

When two married agents from the FBI take over an investigation, Catherine and Vincent hope they are seeing a future version of themselves but fear their work schedules are jeopardizing their relationship. When the two couples bond and team up on the case, a mysterious coincidence surfaces that raises suspicions. JT investigates whether he has super powers of his own while Tess considers a career move. Meanwhile, Heather offers up an interesting option to make her big sister’s life a little easier.

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.

Vincent and Cat are prepared to make the final sacrifice to halt an attack and eliminate beast makers from the world once and for all.

After she's seemingly stood up by Vincent, Cat wonders if it's because he saw her kissing Evan at her birthday. Actually, Vincent mysteriously blacked out on his way to meet Cat, and is now searching for answers. Cat's case pulls her into the sophisticated world of the SoHo art scene. When Vincent finds Cat all dressed up to go to a gallery opening -- with Evan -- he has to admit that his feelings for her are growing deeper. All the while Evan makes his affections for Cat known, leaving Cat torn between the two very different suitors.

JT suspects that Catherine is the trigger of Vincent’s blackouts, so to disprove this theory, Vincent allows JT to inject him with endorphins and sedatives that force him into a fugue state. In flashback, Vincent recalls his time in Afghanistan when he received his first super soldier shot, and remembers who injected him with the DNA altering substance. He also recollects how the other soldiers experienced unpredictable side effects, including fugue states, and is relieved to know that Cat isn’t causing his blackouts. Vincent shares his memory about Murifield with Cat, who experiences some recollections of her own. Then, as Cat and Tess investigate the attempted murder of a teen pop star, Evan suspects that Cat is deliberately protecting the vigilante who saved him in the subway.

Vincent barely escapes being caught by his former fiancée, Alex and must deal with the repercussions of his past. While Cat is in the hospital, she is forced to confront her feelings for Vincent. Meanwhile, J.T. gets a surprising visitor asking about old research he did on mutant DNA.

Cat is forced to reveal things that she had been keeping from Tess to salvage their relationship, and to protect Vincent. Gabe is suspicious of everyone in the department, while Evan witnesses Cat doing something that changes his opinion of her, making him even more determined to track down the beast.

Gabe comes clean to Cat that he knows about Muirfield. Vincent does not think Cat should trust Gabe and is suspicious of his intentions, which causes tension between them. Meanwhile, JT and Vincent finally find a new place to live.

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.

Three months after Vincent Keller was abducted by Muirfield, Detective Catherine Chandler, is reunited with him - but not in the way she planned. He's changed: his scar has disappeared, his memory has been wiped clean and he returns as a supercharged beast on a mysterious mission. Catherine needs to unravel the reasons behind Vincent's change if she has any hopes of recovering their epic love, while also trying to solve the secrets that swirl around her own life.

Vincent and Cat discover that there is another nemesis out to get Vincent, which brings the gang closer together in more ways than one. Cat and Vincent are forced on opposite sides of the law, which puts their relationship in jeopardy.

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.

JT throws Vincent a surprise bachelor party. Unfortunately, it is interrupted by a mysterious sniper with his sights set on putting a stop to Vincent and Cat’s interference with the super human experiments. Cat’s family comes to town for a bridal shower arranged by Heather but Cat is distracted by having to visit her imprisoned father to ask for his help.

Vincent and Cat decide to elope in order to draw out a superhuman assassin chasing them. J.T. tries to find a lead on the experiments, and Heather tries to focus at her new job.

While attempting to be normal newlyweds, Cat and Vincent grapple with how to overcome the danger lurking. They find themselves in the fight of their lives when their happiness becomes jeopardized.