Villainous adulteress Karen Folson
Dr. Karen Folson (Amy Hargreaves) is a villainess from "Leap of Faith," episode 2.13 of Blue Bloods (airdate February 10, 2012). She is an anesthesiologist and the mistress of Charles Bynes.
In the episode, Claudia Bynes, Charles' second wife, was found dead in her bedroom, with Claudia's daughter (Charles' stepdaughter) accusing Charles of killing her mother, claiming that God told her so. Suspicion fell on Charles after learning that his first wife died of an apparent suicide, though it later fell on Claudia after her mental instability was revealed by Charles. Regarding Karen, her encounter with detectives Danny Reagan and Jackie Curatola saw her claim that she and Charles had a doctor-patient relationship, though Danny clearly figured out that they had been seeing each other.
Danny and Jackie's second encounter with Claudia focused on her conversations with God, which later saw Claudia blurt out "Berlin," during her latest conversation. The pair thought they were referring to the city, but Jackie informed Danny that Berlin was also a name, and it led to Harold Berlin, a patient of Karen's who died a few weeks prior. As it turned out, Berlin was set to be operated on by Karen, but as Danny would learn, the fentanyl that was sent to be used for the operation went missing and wasn't returned on time. Danny and Jackie's visit to Charles' apartment, where Karen was found dining with him, ended up revealing everything.
Shortly before Berlin's planned operation, Charles approached Karen for fentanyl for his herniated disc, and out of her love for him, Karen took the fentanyl and gave it to Charles for his own use. During her reveal, Karen stated that she warned him about the drug, stating that it could cause a heart attack, and it was after hearing the last part of Karen's warning that Charles switched Claudia's medication for multiple sclerosis with a batch he laced with fentanyl, with Claudia fatally succumbing after injecting herself with the drug. Though Karen's role in Claudia's death was inadvertent, her villainous actions intentionally led to the death of Berlin, and she was later arrested (off-screen) for participating in the sale of a medical drug.