A deadly subway collision is investigated as a New York City medical examiner attempts to discover the truth behind his inexplicable immortality.

After Henry pegs the case of a would-be bridge jumper as a homicide while the police label it a suicide, he and Jo go on a rogue investigation for proof. Meanwhile, Henry's anonymous caller surfaces again. Apparently, he has been tracking him for years. A letter on antique stationery might provide Henry a fascinating clue about the caller, and he enlists Abe's help in tracing the note's history to a foreign locale. Revealing flashbacks unveil the beginning of Henry's great love affair with his soon-to-be wife, Abigail.

Henry and Adam have been on a long, unrelenting collision course, which is about to come to a head – possibly bringing about one man’s death – with only Jo standing in the way. Henry and Jo’s murder investigation into a museum worker’s death centers on a priceless missing ancient dagger, which not only ended the life of Julius Caesar, but also killed Adam the first time. Meanwhile, Adam knows that there is something that Henry fears more than death – that Jo might discover his mystery. The two men tangle in a tumultuous game-changing confrontation. But at long last, will Jo finally learn about Henry’s secret?