(Strip Number 1373, Original Publication Date, 23 November 1988)
Panel 1: After handing Martha the note, Michael tells her not to open it. At this point you have to begin to wonder if he has somehow booby-trapped the note and is having second thoughts about booby-trapping it. The dialogue works pretty well for that situation.
Panel 2: “I mean don’t open it in here!” (where the booby trap will be set off and get me too.) In the meantime, Lynn has forgotten that her square in the background is supposed to partially represent where the wall ends at the ceiling and she has drawn a silhouette man whose head goes above the ceiling.
Panel 3: “Um...open it when you’re somewhere alone. I don’t want anyone but you to read what I wrote in there.” (That way you will be the only one affected by the booby-trap.)
Panel 4: “On second thought, maybe I’ll just take it back!” (What am I doing? I don’t want to hurt Martha with my booby-trapped note. I must take it back.)
Summary: After all this, if I were Martha, I wouldn’t open that letter. What is in this letter that Michael feels needs to be treated as a need-to-know, top secret clearance letter? We will never find out, but based on Martha’s response letter coming up, Mike is saying something along the lines of “I like you.” That's not much of a secret considering that everyone already knows this from the last storyline.