Though I like the idea of face to face "right in the eyeballs" approach (it will show my demeanor), I could also launc it as a text to her once I know she is in the vehicle with OM.
That could create an interesting drive.
Of course, I will be unavailable for a day.
That is EXACTLY how it's done.
There'll be plenty of time for face-to-face later on. The idea of this tactic is to completely RUIN their little planned weekend.
I did this once to my wife (it was only a few-hour potential hook-up), and it worked to great effect, judging from what I heard later on the voice-activated recorder.
It's even BETTER if the cheating spouse is planning on taking a PLANE TRIP to meet their lover. Then, you can lob your grenade when they're ON THE TARMAC, getting ready to take off, and they can't even CALL THEIR O.P. -- or anyone else -- UNTIL THEY LAND!!!