Christmas, 1669. In the grip of the coldest winter for years, the River Thames is frozen from bank to bank and London celebrates with a traditional frost fair held on its broad back. Revellers come from far and wide to enjoy the spectacle. Among the throng is ambitious young architect Christopher Redmayne. By chance he meets a good friend, Constable Jonathan Bale, attending with his family. As the adults talk, Bale’s sons skate around them. But their competitive nature spells trouble onto thin ice and is in danger of crashing into the freezing water below. Christopher and Jonathan save the boy but make a chilling discovery – the frozen corpse of a naked man embedded in the ice. Bale vows to investigate but Christopher sees no reason to involve himself further until his own brother Henry is accused of the murder and thrown in jail. Now Henry faces execution if Christopher cannot prove his innocence. The architect must risk all he holds dear, both professionally and personally, to uncover the truth.