The Golden Hour — Maiya Williams

In this "page-turner debut" (Kirkus Reviews), thirteen-year-old Rowan and his friends, twins Xanthe and Xavier, find a time portal in an abandoned resort hotel. They travel back to revolutionary France, in search of Rowan's mysteriously missing sister, Nina. A desperate dash through Versailles and a daring escape from the guillotine are just two of the many adventures the children tackle as they race against time. If they don't make it home with Nina by the "golden hour," they won't come home at all.