The Identicals by Elin Hilderbrand

Harper and Tabitha are identical twins who, like the twins in Parent Trap, were split up when their parents divorced and have been estranged for years. Harper, who grew up with their laid-back father, has a much more casual lifestyle involving a lot of low-paying jobs and an erratic romantic life. She lives on Martha's Vineyard. Tabitha, who grew up with their fashion designer mom, had a much more structured, restrictive upbringing. She lives on Nantucket. Now she is a single mom with a handful of a teenage daughter, Ainsley. When their mother, Eleanor, breaks a hip, Tabitha has to go off to Boston to take care of her. So Harper comes to Nantucket to take care of Ainsley and run Tabitha's clothing store. Once Eleanor is on the mend, Tabitha decides to go to Martha's Vineyard to rehab their late father's house. In effect, the two sisters switch lives. With unexpected consequences for both of them.

This was a totally entertaining romp and a perfect summer book.