Jersey doubles in size when the tide goes out. Helen Mark discovers what the retreating waters reveal, from the evidence of our Neanderthal ancestors to the extraordinary marine life of the island's reefs.

At La Rocque three local guides take her across miles of treacherous shifting sands to Seymour Tower, built to defend Jersey against the French but used by the German occupiers. On the north coast she meets Dusty, the first red-billed chough to be born in the wild in Jersey for a hundred years and in the south-east she searches for evidence of the Neanderthal people who left more evidence of their existence here than in the rest of the British Isles combined.

Producer: Alasdair Cross.