Linda Lavin (Anna) is the matriarch. Staunch, ignored, marginalized, Jewish, and mildly bitter. Greg Keller (Seth) is an obituary writer - lonely, preppy yet schleppy, nebbish, and gay. Kate Arrington (Abby) is the less than happy, hippie, gentle, and lesbian. Ms. Lavin is the perfect choice to play a Jewish mother lording over her children in a loving yet authoritative and sarcastic sort of way. Mr. Greenberg seems well skilled at constructing the damaged, delicate, off-balance, and less than perfect family. His language is rich and often the choice of words is argued over and debated in the dialogue. It's smart and swift. His ability to effortlessly sail through the story-telling is large. Sometimes it's too large and we get bogged down - such as the latter half of Act II.
It turns out that Anna has indeed had what the title suggests - a brief affair. Her children may or may not have been aware of it but they are grappling with it now. Her son is having the most difficulty coming to grips with the reality of the beans his mother is spilling. The affair is quite a shocker. Well, it's a shocker only after they employ a theatrical device to turn up the lights break the 4th wall and have the two children explain to the audience what their mother just admitted to. I doubt many people would simply recognize the name David Greenglass. The use of this abrupt device - is used to a lesser extent throughout the show - as this is really a memory play, a story told by the two children intermixed with flashback scenes from their life.
Tender, tough, heartbreaking, funny, and warm all at the same time. In the end, the message is summed up by Anna to her son by explaining all she ever wanted was to be remembered.