Twelve-year-old Ali is excited by the prospect of spending the summer at Sycamore Lake, babysitting her four-year-old cousin Emma while her Aunt Dulcie paints at the newly renovated, long-deserted family cottage. But who is the neighbor girl “Sissy,” who wedges herself like a thorn between the two girls? Who is “Teresa,” the girl torn out of a family photograph, and who all the town seems to know about? Why does Ali’s mother refuse to come to the cabin, and why do Dulcie’s paintings suddenly take a dark and watery tone? Signature spooky Hahn sends appropriate shivers up the reader’s spine. If Ali’s insights into Sissy’s psychological problems are surprisingly mature, they’re necessary to render the reader’s delightful fright into a satisfyingly chilly but calm resolution. Not terribly surprising, but it does the trick. (Fiction. 9-13)