First broadcast 23rd September 1970.

Is an eminent scientist, on lone to a top-secret research establishment, a security risk?

Derren Nesbitt ... Det. Chief Insp. Jordan
Fulton Mackay ... Det. Chief Supt. Inman
Morris Perry ... Charles Moxon
William Lucas ... Dr. Clifford
Alethea Charlton ... Brenda Clifford
Emrys Jones ... Falcon
Ania Marson ... Karin
Maureen Davis ... Gillian Heyman
Ronald Russell ... Sir Hugh Lodge
Denis Goacher ... Schaeffer
John Moore ... Yachtsman