An old hermit claims to have seen a ghost in the graveyard on the estate of the sixteen Duke of Benedict. Steed and Emma question the locals, and the Duke, about a mine disaster of five years previous that apparently killed the Duke's predecessor and fifteen other men. After Emma disappears, Steed ventures down into the mine and discovers something much larger than anyone on top ever imagined.

An interesting story with what was becoming the standard amount of eccentric characters, and an excellent guest cast headed by Julian Glover, but the story bears similarities to The Town of No Return with a slightly higher budget.

Responding to someone pointing out the exit from the underground city, Steed remarks, "Exit, from the Latin 'exodus' meaning 'to leave or to depart'." That's completely wrong... "Exodus" is actually a Greek word, "ex" meaning "out of" and "hodos" meaning "way." Thus, "exodus" means "a way out [of somewhere]." "Exit," on the other hand, is pure Latin: "ex" meaning (once again) "out of" and "ire" meaning "to go." To be more precise, "exit" is the third person singular of the present indicative, or "he goes out." (Remember your stage directions? "Exit" for one actor; "exeunt" for two or more.) (Submitted by fellow Avengernaut Margaret Warren, a former English teacher, in case you were curious...)