Samantha Kaye (Cristina Rosato) is the hidden villainess of "The Devil Inside", episode 4.11 of Republic of Doyle (airdate April 14, 2013). She was amongst a group of civilians and police officers taken hostage by Charles Alomar, who came into the station with a bomb strapped onto him that was hooked up to his heart rate, which would go off if it got too high or low. It also appeared that Charles was acting in revenge of the death of his brother, who had been arrested with selling drugs to an undercover cop.
Over the course of the episode, Samantha appeared to be a nervous and terrified woman, but this was ultimately revealed as a mask for her true conniving nature. As revealed in the episode's climax, Samantha was the true mastermind behind the hostage situation, having tied up and strapped Charles' ex-wife Julie Cameron to a bomb (later revealed as a fake), later strapping a real bomb to Charles after knocking him out and forcing him to take the police station hostage under the threat of killing Julie. Her motivation was related to her profession as a drug dealer, having had Charles' brother as her driver. When Samantha learned that her driver had stolen her product and was planning to get in on the business himself, she had him killed within prison and orchestrated her current plot to retrieve the GPS unit she could use to find her truck (and presumably her drug supply).
Samantha's villainous reveal came once Julie was found by Malachy and Rose Doyle at her house alone strapped to the fake bomb, confusing Jake as to who was behind the operation (having learned from Charles how he had been forced into taking the station hostage) until he remembered how Charles had been instructed by the mastermind to take him and Samantha to the evidence room. Samantha then officially revealed herself as the mastermind by walking into the evidence room, where Jake was with Charles and Des Courtney, armed with a pistol. Samantha then deactivated the ticking bomb before having Charles call the police and claim he was going to kill the hostages if they didn't clear the premises, while also claiming full responsibility for the hostage situation.
Samantha then forced Jake and Des to search for the GPS unit in the station, while revealing her past with Charles' brother and how she'd organized the death of his brother. After Jake found the unit, however, the evil Samantha turned the bomb back on and planned to escape while posing as the sole surviving hostage, later claiming she had managed to slip out and painting Charles as a vengeful psychopath preparing to kill everyone in revenge for his brother. When Jake and Des were able to free Charles from the bomb and escape the blast, however, Samantha attempted to escape, only to be caught and disarmed by Jake as Leslie cornered her. Samantha was then handcuffed and arrested by Leslie, while telling Jake he had no idea what he was doing.