Detective Catherine Chandler is a smart, no-nonsense homicide detective. When she was a teenager, she witnessed the murder of her mother at the hands of two gunmen and herself was saved by someone – or something. Years have passed and while investigating a murder, Catherine discovers a clue that leads her to Vincent Keller, who was reportedly killed in 2002. Catherine learns that Vincent is actually still alive and that it was he who saved her many years before. For mysterious reasons that have forced him to live outside of traditional society, Vincent has been in hiding for the past 10 years to guard his secret – when he is enraged, he becomes a terrifying beast, unable to control his super-strength and heightened senses.
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.
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.
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.
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.
Liam’s shocking history makes Cat delve deeper into the Ellingsworth family, where she learns of their tragic past. Vincent and Cat realize that they will need to use their secret weapon if they want to take Liam down. Meanwhile, JT has a theory about how to save himself but it involves none other than Liam.
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.
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.
Desperate to start over with Cat, Gabe tries to woo her by taking her on a romantic date. However, she has plans of her own regarding how to save Vincent – while also trying to plan Heather's bachelorette party.
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..
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 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.
Cat's sister Heather drops by for a surprise visit at the worst possible time, just as Gabe suspends Cat and Tess from the squad in an effort to force Vincent out of hiding.
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.
With Vincent in hiding and Cat's job on the line, they must re-group about how to bring down the people hunting beasts. Vincent tries to infiltrate a private army, while Cat scrambles to obtain information and hopes that no one at work discovers her ulterior motives.
When Cat and Vincent make it their mission to capture Liam, they find information about a Patient X that they might be able to use to help them find him. Meanwhile, JT and Tess work to confirm that JT is serum free.
Cat and Vincent must work together to save J.T. when he gets kidnapped, while Tori attempts to intervene, with fatal consequences. Meanwhile, a stranger from FBI Agent Dana Landon's past is rescued along with J.T., and might have some insight about Vincent's beastly past.
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.
Vincent and Cat find themselves at odds on how to deal with Agent Reynolds, which forces Vincent to wonder if he is more beast than man. Cat makes a drastic move that will forever change her relationship with Vincent.
When Vincent becomes the subject of a city-wide manhunt, he and Cat try to stay below the radar. But they find a surprising ally when the FBI approaches them about helping on an important case.
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.
Vincent is forced to undergo a series of tests orchestrated by the mystery buyer in order to keep from being exposed. Cat, JT and Heather work to exonerate Vincent.
Cat confronts her birth father about the mysterious role he's played in her life, while Vincent has to neutralize a high-profile beast. In the process of doing so, Vincent finds himself rescuing Tori, a damsel in distress, who may be the key to completing his mission.
Cat and Vincent take Agent Knox's offer to extricate and try to lead normal lives -- but forces out of their control conspire to expose them and drag them back into the fray.