Squishy and her twin stepsisters, Vee and Jessie, are on the trail of a mystery; it starts with "Boring Lady" working in her office across the street at 2:57 in the morning, continues with the trashing of Mr. Hinkenbushel's apartment next door, and apparently involves illegal diamonds--and Squishy becomes convinced that Mr. Hinkenbushel is the diamond smuggler, only none of the grownups believe her.