Safe and Sound by Fern Michaels

Isabelle Flanders Tookus isn’t expecting to involve the Sisterhood in a new mission when she strikes up a friendship with a curly-haired boy in her local park. Ben Ryan is an eight-year-old child genius, the grandson of millionaire Eleanor Lymen, who hired Izzy years ago to design an institute for gifted children. Ben’s mother passed away and Ben now lives with his stepfather and his wife. They’ve been using Ben’s trust fund to support their lavish lifestyle while shamefully neglecting Ben. And with the wife getting greedy, Ben’s safety is now in jeopardy.
 
Izzy’s first step: call in the Sisterhood. The second: track down Eleanor, who has mysteriously vanished on a secret mission of her own. Izzy, Annie, Myra, and the rest of the Sisters come together at Pinewood, thrilled to be united once more. Together they’ll lay a trap, one that will protect Eleanor’s beloved grandson, get him into the happy home he deserves, and provide the kind of creative, satisfying payback the Sisters dish out so well . . .