In the early 1920s, six Londoners decide to cast themselves in the roles of pilgrims and go to the small island off the northwest coast of Wales called Bardsey island--or in Welsh, Ynys Enlli. Each of these men has his own reason for wanting to do this. Some of them go on this journey in the spirit of scientific inquiry, some to expiate personal demons, and one (Professor George Edward Challenger) to disprove the beliefs the others have in the existence of spiritual beings--ghosts. In the process of their "pilgrimage," each man has dramatic experiences that make him a changed man upon his return to London.