Legends surround this tiny island off Cornwall's south coast, including a visit by Christ himself, brought here by Joseph of Arimathea from distant Glastonbury. The team are out to discover the truth behind the myths. Could this island have witnessed the birth of Christianity in Britain? They are hampered by the tide, which limits the time allowed for digging. Previous digs have linked the now-vanished St. Michael's Chapel on the hill to the Celtic dark ages following the Roman occupation. It would certainly have been a beacon for pilgrims and overseas traders through the ages; and there are tantalising hints of prehistoric activity. The chapel seems to be mirrored by a similar structure on the mainland, which the team are also attempting to excavate. They are joined by historian Nicholas Orme, Oliver Creighton from Exeter University and Finds specialist Carl Thorpe. Investigating possible wrecks are two divers from the Royal Navy.