(Strip Number 671, Original Publication Date, 2 August 1984)
Panel 1: We find Mike on the phone telling Elly that he's fine and havin'a great time.
Panel 2: He an'Grampa went fishin'an'went to the zoo an'the beach an'to the water slides.
Panel 3: Tomorrow, they're goin'to the planetarium an'to have dinner.
Panel 4: When he asks if he can stay forever, Jim and Marian look as if they've aged about fifty years or so.
Summary: This, I think, is because they think that they've done their time in Hell parenting his lunatic mother. Also, their fear that she's trying to get them to raise her kids for her because she's too big a wuss to cope seems to be a reality.