Synopsis: It's happening again! Despite their vow to each other at the end of Once Every Never, best friends Clare and Allie once more find themselves in trouble—and travelling in time. Indulging in a low-key vacation at Glastonbury Tor, taking part in an archaeological dig while soaking up the sights of summertime England, the girls have promised each other: no time travel shenanigans; no involvement with dangerous Druids or villainous museum thieves; and definitely no weirdness about the fact that Clare is now seriously dating Milo, Allie's super-genius hottie cousin! But when Allie makes an unexpected discovery at the dig site—a skull—the grisly artifact sends her spiralling back in time to a Roman encampment besieged by rampaging Celts. Caught between the Legions and the war band, Allie is rescued from certain death by Marcus, a young Roman soldier with a secret. As she struggles to survive in the past, Clare and Milo race desperately against time in the present to bring Allie home...before she loses her head OR her heart