ObscureHollywood.net’s review published on Letterboxd :
During WWII, an independent Scottish inventor (Leslie Banks) is perfecting a bombsight for British use against the Germans. The inventor has a talented assistant (Michael Wilding). His property includes his large home, his laboratory, and a cottage. His wife (Jeanne de Casalis) has listed the cottage for rent. Eccentric Alastair Sim has rented the cottage and moved in. The cottage is also used as a hospital for an injured pilot (John Mills). A teenage evacuee (George Cole) is staying in the house. The butler is actually a Scotland Yard policeman assigned to protect the inventor. Among the people living on the property are Nazi agents intent on kidnapping Banks. As intrigue swirls around the inventor, the identity of the Nazi is not revealed until the end of the film. The Nazi agent is shot to death and has an over-the-top death scene, which he presumably enjoyed enacting.
A semi-comic story of WWII intrigue moves briskly and amusedly under the direction of Anthony Asquith. The film is worth watching just for the great cast of British actors.