LOS ANGELES — John Lithgow was going to pass on the chance to play serial killer vs. serial killer on Dexter, with an Italian vacation, cruise and his son’s wedding awaiting him.

He made it to the ceremony but postponed the trip, and he credits his wife of 28 years with pushing him into the plum job.

“She’s the one who said, ‘No, you’ve got to take the role,’ ” he recalled.

Lithgow guest stars as Arthur Mitchell, the so-called Trinity Killer whose victims come in threes and who both repels and attracts Michael C. Hall’s Dexter Morgan in the Showtime drama.

Tempted to learn how the Trinity Killer has evaded capture, Dexter begins to make mistakes as he deviates from his protective “code,” leading to a plot twist in the episode, “Slack Tide,” that aired Sunday.