''Two years after my mother died, my father fell in love with a glamorous blond Ukrainian divorcée. . .She exploded into our lives like a fluffy pink grenade,'' recounts Nadia, the British-born daughter of Ukrainian immigrants. Seeking to protect Pappa from someone she's sure is a gold-digging tart, Nadia forms an uneasy alliance with her estranged older sister. Yet despite their strenuous efforts, Pappa marries Valentina (who's 36 to his 84). Not-so-hilarious complications ensue, many of them familiar to anyone who's witnessed the ravages of age. ''There's no fool like an old fool'' appears to be the theme here, but Lewycka skillfully teases out a more complex story, underpinned by Ukraine's horrors under Stalin and Hitler. As Nadia discovers when she delves into her family's past, ''maybe there are some things better not known.''