Shackles from the deep

A pile of lime-encrusted shackles discovered on the seafloor in the remains of a ship called the Henrietta Marie, lands Michael Cottman, a Washington, D.C.-based journalist and avid scuba diver, in the middle of an amazing journey that stretches across three continents, from foundries and tombs in England, to slave ports on the shores of West Africa, to present-day Caribbean plantations.