 Experimentation had largely been forbidden for fear of losing valuable couriers before, but with their base in the United States under threat, the Clan needs to seek out alternative options.Huw and his team discover that the Lee family Locket, while ineffective in Massachusetts and New York in the United States, works in Maryland, and leads to a fourth world in the grip of an Ice Age with polar sheets covering the northern States.The fourth world (Timeline 4) is seemingly empty, but shows signs of a highly advanced, dead civilization.