(Strip Number 7127, Original Publication Date, 31 October 1982)
Panel 1: We start things off with Mike, who's about to go trick-or-treating, acting like he's a plane about to take off.
Panel 2: His good mood collapses when an off-camera voice tells him to wait and not go out yet.
Panel 3: Elly who was the person telling him to wait tells him that he wants him to take Lizzie trick-or-treating and to wait for her to join them; Mike, who spends enough time watching Lizzie as it is, whines in disappointment.
Panel 4: He then rumbles "BOY!! On Halloween!! I gotta go out with my dumb sister!!"
Panel 5: As he, Lawrence the clown and Lizzie come up to their first house, he stares at her all Gorey-eyed and menacingly tells her that she jes'better not cramp their style
Panel 6: Mrs Baird gushes about how sweet it is to see a brother taking his sister trick-or-treating and hands the two of them a bit extra.
Panel 7: Steve tells Mike to take two handfuls because he's being a guy for taking Liz with him.
Panel 8: Elly shows up and says that she's here; this presumably means that she's going to take Lizzie of Mike's grubby hands.
Panel 9: She frowns in confusion when Mike says he's going to keep her.
Summary: That's because she forgot that Mike likes candy and will endure anything to get more even if that anything is the sister who has the mistake on her of not being the brother he won't admit he would have resented too. Speaking of not admitting things, the whole point of the tweak Lynn did was to ensure that the Halloween strip fell on Halloween; since Monday's strip ran on the 30th back in the day, she sort of failed.