London, 1939. Middle-aged spinster Guinevere Pettigrew, whose attitudes and behavior are shaped by being a vicar's daughter, may not have the correct temperament for her chosen field of governess, having just been fired for the third time for not following the orders of her employer, right or wrong, she leaving this most recent employ out of circumstance with no money and only the "funereal" clothes on her back. With this a third strike, her employment agent, Miss Holt, refuses to represent her anymore. Desperate for another governess job if only to put food into her stomach, Miss Pettigrew, on a few mistruths, is able to finagle her way into the employ of flighty and disorganized American Delysia Lafosse, who Miss Pettigrew eventually learns the hard way is not wanting a governess but rather a social secretary for which Miss Pettigrew has no experience. Delysia, a singer, is trying to break onto the West End stage if only as a springboard to Hollywood stardom in films. The role of Delysia's social secretary, at least in this first day, is to manage her sex life, she having three men on the go: Nick Calderelli, the owner of the nightclub where she performs in a cabaret act and in whose lavish flat she lives; impresario Phil Goldman who is considering her as the lead for his next West End musical; and Michael Pardue, her penniless pianist in the cabaret act, he who has just been released from prison. An associated side job which Miss Pettigrew has no other option but to accept is for Delysia's acquaintance Edythe Dubarry, an upscale ladies fashion retailer who wants Miss Pettigrew to convince, without he not not knowing that he is being manipulated, her on again/off again - currently off again - boyfriend, ladies undergarment designer Joe Blomfield, to reenter into their called off engagement. Miss Pettigrew doing this task is despite she knowing that Edythe's interest in Joe is more professional than personal. Miss Pettigrew, working on Delysia's directive, may have her own views on what, or more precisely who, she should do as the one and only. In the process, Miss Pettigrew may also have some views on what she is doing for Edythe. The imminent war, which had been in the back of the minds of the general populace, becoming more of a reality may factor into what happens with this collective.