When she was a teenager, Catherine Chandler witnessed the murder of her mother. Cat would have been killed too, but someone – or something – saved her. Now, years have passed and Cat is a police officer, investigating a case that leads her to the person who saved her: a doctor named Vincent Keller. With the help of his childhood friend J.T. Forbes, Vincent has been in hiding, guarding his secret — when enraged, he becomes a terrifying beast, unable to control his super strength. Still, Cat is touched by the person that lives within the Beast and she knows she has to keep her relationship with Vincent a secret from her boss, Joe Bishop, her partner, Tess Vargas, and even from her close friend, Evan Marks, the medical examiner. Cat and Vincent are powerfully drawn to one another, but they understand that their connection is extremely dangerous for both of them.

When a rising young ballerina mysteriously falls to her death, Vincent senses that the understudy, is hiding information about the dancer’s murder. Meanwhile, J.T. worries that Cat’s visits to the warehouse loft leave Vincent vulnerable to discovery by Muirfield’s agents. Catherine encourages Vincent to help her investigate deeper into the Muirfield project, but when Vincent refuses, Cat investigates on her own. Tess tries her hand at dating again, but soon discovers that she’s unknowingly involved with a married man. Heather moves out of Cat’s apartment after growing uncomfortable with her sister’s quest for more answers about their mother’s death.

Iris, a Bosnian immigrant, is arrested on the suspicion of killing a judge for deporting her brother. Vincent insists that Iris is innocent, so trusting his instincts, Cat works behind-the-scenes to uncover the truth. When Cat's actions disrupt the investigation, Joe places her on leave. Nevertheless, she continues on her own to discover that Iris is hiding a family secret, and needs Vincent's help. JT is concerned that Vincent risks exposure to Murifield by helping Cat, leading Cat to work out a way to communicate with Vincent without seeking him out.

Vincent revives a 19-year old boy who was left for dead in a dumpster and rushes him to the E.R., where he remains in a coma. After Evan declares that the boy's x-rays reveal a history of bone fractures, Cat and Tess question the father, Zachary Holt, who worries that his son's ADHD and history of fighting and gambling might have gotten him mixed up with the wrong crowd. Meanwhile, Silverfox and his Murifield agents track down Cat, and offer to tell her the truth about her mother in exchange for turning over Vincent, who they insist is a monster. Cat tells Vincent about her Silverfox encounter, and Vincent realizes that Cat might be afraid of him. JT wants them to flee, but Vincent refuses to leave Cat, instead offering to surrender to Silverfox in exchange for Cat's safety.

Vincent is captured on a convenience store surveillance video while preventing a robbery, and Cat warns him to be extra careful when his photo appears in the newspaper. Cat and Tess investigate the disappearance of a woman named Amy who has gone missing after her fiancee, Dr. Michael Walters, surprised his bride-to-be by placing their engagement announcement in the paper that morning. Cat wonders if her disappearance was intentional after Vincent mentions that he and JT have an escape plan to clear out of their loft without a trace in a matter of minutes. Meanwhile, Heather is planning a surprise birthday party for her sister, forcing Cat to postpone her birthday plans with Vincent.

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 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.

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 Muirfield 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.

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.

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.

Vincent is torn between his new feelings for Cat and his old memories with Alex. 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.

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 with the truth about his past. Evan realizes that Claire, the woman he is dating, is hiding things from him. Heather meets and falls for Joe's younger brother Darius, and Vincent tries to win over Cat with romantic gestures for Valentine’s Day.

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.

New Assistant District Attorney Gabe Lowan arrives at the precinct, suspicious that cases involving the vigilante are being mishandled, and wanting answers. Cat is determined to protect Vincent at any cost, which includes tracking down a witness and threatening him at a gala masquerade ball. Meanwhile, Vincent worries he may lose control if he gets romantically involved with Cat.

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.

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.

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.

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.

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.

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.