ABOUT THE CHARACTERS:
Catherine: Basically, Catherine is a homicide detective who was nearly murdered by the men who killed her mother but some type of "beast" saved her.
Vincent: He was a soldier in the army and was also a part of the Operation Muirfield, which was an experiment that turned the army men into super-soldiers. His ability was to turn into a very human-like creature but with a beast-like mind. The army was then shut down because the subjects were out of control but Vincent survived and went into hiding in New York but came out when he fell in love with Catherine the girl whom he saved nine years ago.
J.T.: A childhood friend of Vincent who signed him up for the Muirfield program thinking that it would do more good than harm and also a professor at NYU.
Tess: Catherine's partner and closest friend who eventually discovers and reluctantly agrees to keep Vincent's secret, though eventually she learns to trust and form a friendship with Vincent, if only for Cat's sake. She had an affair with her boss, Joe Bishop, but later begins a relationship with J.T following his departure from her precinct.
Heather: Catherine's younger sister and former roommate, who moves to Miami to further her career, but later returns to New York engaged to be married. When she first met Vincent she immediately hated him, but near the end of Season 2 Catherine admits, with Vincent's blessing, their secret. At first, Heather is angered and horrified by her sister's lover; however, she has a change of heart when Vincent willingly risks his life to save hers.
Gabriel: A former assistant district attorney who came to Catherine's precinct to hunt down Vincent. He was eventually revealed to be a Muirfield experiment, as well, trying to become human. He tries to kill Vincent to save himself, but becomes human when Catherine revives him after he is supposedly shot dead. In Season 2, he tries to make amends because he is falling for Catherine. Catherine starts dating Gabe after she and Vincent break up. When Catherine leaves Gabe to be with Vincent again, Gabe becomes obsessed with getting her back, eventually changing back into a beast to get Vincent away from Catherine. He is killed by Catherine in self-defense.
Joe: Catherine and Tess's former commanding officer. He cheated on his wife with Tess. His vendetta against his brother's killer (Vincent, by accident) distracted him from his job and he was fired by the start of season two.
Dr. Evan Marks: Police morgue medical examiner who worked with Catherine and had a flirtatious relationship with her. Evan worked with Muirfield to capture Vincent out of a mixture of fear and jealousy for Catherine; when he realized Muirfield had tricked him, he helped Vincent and Catherine escape, but was killed by Muirfield agents.
Tori Windsor: A beast who was actually the daughter of a Muirfield experiment. After Vincent killed her father, she found out she possessed beast abilities, and became attached to Vincent because of this. She tried to form a deeper wedge in the feuding between, and separated Vincent and Cat because of this attraction; Vincent eventually dated Tori for a while. She later lost her life trying to prove herself to Vincent; she died in his arms apologizing, and blessing Vincent's love for Catherine.