Escape from Holy Island

The history books tell us that on the 8th of June, 793 AD, the Holy Island of Lindisfarne was burnt to the ground by Viking raiders. But history also records that "fiery dragons were seen flying in the sky" - can that be true? With time running out, the Doctor, Peri and a young HG Wells mobilise the island’s monks as the real raiders of Lindisfarne thunder over the North Sea - and they don’t look like Vikings...