Fruit of the Poisonous Tree (1) (S04E01)

While Frank is in Washington discussing his return to work with Paul, he receives a call from Dan informing him that Vinnie has missed his latest check-in. Concerned, Frank heads to Vinnie’s home, where he discovers signs of a kidnapping. Ignoring Paul's protests, Frank takes it upon himself to investigate, learning from Carlotta that Vinnie was probing the mysterious death of a priest in El Salvador. His search leads him to Miami, where he encounters Michael Santana, a disbarred federal prosecutor and Vinnie's last contact. Santana denies knowing anything about Vinnie's fate. As Frank digs deeper, he uncovers a CIA operation and is warned to cease his inquiries.