 When the police and the civil authorities suspect that petrol is being stolen from a local depot, Foyle agrees to let Sam Stewart go undercover as a driver to see if she can find out what is going on. Sam is partnered with Connie Dewar who is in love with a flying officer, Rex Talbot who just happens to be Andrew Foyle s best friend. It becomes apparent to Sam that Connie is involved in the petrol thefts and when she if found dead, there are any number of suspects. Connie is also several months pregnant but she didn t tell anyone who the father was. For DCS Foyle, the case becomes especially complicated when it turn out his son Andrew was perhaps the last person to see her alive.