Every day, on a sandy beach or a rocky foreshore, fascinating evidence of Britain's island history appears and disappears as the tide rolls in and rolls back out again. Tori Herridge and Alex Langlands reveal stories from our extraordinary maritime, industrial and natural history. In Essex, Tori and Alex investigate the earthwork remains of a fort dating to the time when Henry VIII took England out of the European Catholic union. They pay their respects to some Thames sailing barges that are now sunk in estuary mud but which were once the glory of the east coast. And they find a First World War German U-boat stranded in a tiny creek.