Father Brown and Mrs McCarthy visit the cottage hospital in the village of Standing where many of the children have been struck down by an outbreak of polio. When a local barmaid is found murdered at the local stone circle, her best friend, Ginnie, is arrested for her murder when it is discovered they had fallen out over Ginnie's blaming her for her son's contracting polio.. Unfortunately, the supposed murder weapon that it is hoped will clear her, only seems to strengthen the case against her. Then a local mystic makes a connection between the death and a legend about sacrificing an innocent at the stones - and someone tries to kill Ginnie and make it look like suicide.