Britain’s Department Z faces its biggest test when the organisation is threatened by an enemy within its walls.

Charles Corliss, son of a murdered agent from Department Z, seems like the perfect recruit for the ultra-secret spy organisation. But when things start going seriously wrong, the agents begin to suspect that this charming young man is not as loyal as he first seemed. Filled with hate for the organisation which allowed the death of his father, Charles begins to sabotage the department as a double agent dedicated to the Communist cause.

The Enemy Within is the 25th book in the Department Z series, and was originally published in 1950.