First broadcast 25th April 1978.

Shore finds an underground passageway from the crypt to the tower and discovers a link between the dead nun and a missing schoolgirl.

Maria Aitken ... Jemima Shore
Renée Asherson ... Mother Ancilla
Susan Engel ... Sister Agnes
Sylvia Coleridge ... Sister Boniface
Doran Godwin ... Sister Lucy
Patsy Kensit ... Tessa
Catrina Hylton ... Mandy
Elvi Hale ... Lady Polly
John Bryans ... Sir Charles