When American archaeologist Gerald Smaill uncovers a golden Byzantine cross in cave in Asia Minor, a disembodied voice threatens death. En route back to England via cruise, he receives further threats and confides in fellow traveller Father Brown. A secret crypt beneath a Dover church has been recently uncovered containing the body of a 13th-century bishop mummified in Egyptian fashion, along with a similar golden cross. Smaill, Brown, and several passengers investigate the find and risk the curse that accompanies it.