The Third Doctor is strangely concerned about Professor Horner’s plan to cut open an ancient barrow near the peaceful village of Devil’s End.

Equally worried is Miss Hawthorne, the local white witch, who foretells a terrible disaster if he goes ahead.

The only person who wants the Professor to open to the barrow is the vicar (in truth the Master) whose secret ceremomies are designed to conjure up from out of the barrow a horribly powerful being …