When you've said Martha's Vincyand in the 1840's you've said the best there is to say about Tammy's discovery that she can manage without twin Susan, her concurrent discovery that thievery is what's the matter with Uncle Jonathan's ailing retail business. The girls are separated when Susan stays behind in Falmouth to help Aunt Delia while Father and Mother relocate on the Vineyard with Tammy, who has misgivings about everything from arithmetic to the Gay Head Indians. She's an unlikely twelve, and too nebulous for sympathy anyhow. Which leaves a blatantly obvious villain and some mildly interesting local items like the school taught by whichever sea captain was ashore and the Indians' Thanksgiving celebrated whenever the fiddler was available.