Castle in the Round. At the mouth of the Thames, on the Isle of Sheppey in Kent, lie the remains of Queenborough Castle, built by Edward III during the Hundred Years War. The Time Team excavate the castle mound, but its circular design makes analysis difficult, and opinion is divided whether the castle was built for defence or as a royal bolthole from the plague. The surrounding town is also explored, leading to the recreation of a bizarre journey using a paper boat paddled by oars made of cod.