“Blackmail,” originally aired November 28, 1994. Nostalgia and spoilers within.
A guy who’s having an affair on his wife catches Mac beheading someone AND catches it on tape. Curse you, 20th century. Mac is trying to just do the normal Immortal thing and take out this immortal thug theft/murder duo, but he now has to spend his day trying to find the guy who videotaped him–who wants to blackmail Mac into killing his wife so he can be with his lover. Flawless plan. Mac tries to fill her in on the evil plan, but she’s already watched the blackmail video, so….
Then the guy tries to suggest the “Strangers on a Train” plot, because he realizes Mac wants to kill this other guy. So they can each kill people! FLAWLESS!!! Oh, he is so out of his element. The mortal even tries it and gets killed by Mac’s immortal foe, and we are all unsurprised.
Mac and Joe realize they have to try to talk to the wife before she exposes the video, and the evil Immortal is already there, so maybe that means she’ll believe them. They certainly do destroy the house with the Quickening. She gives Mac the tape, and things go back to normal. Whew, that was a close one. Somebody better be careful about technology in the Immortal world…