In a few words, he changes the subject.
In chapter 2 of Agatha Christie's novel And Then There Was None, some of the guests meet while waiting for a taxi on their way to their mysterious host/employers' home. Vera and Lombard engage in a polite conversation that begins with a classic topic: the weather. She is certain she has been offered a job as a secretary, and although she has never met Mrs. Owen, she is looking forward to spending some pleasant days on Indian Island.
Lombard has too accepted a job, although the nature of it is less clear to the readers. We know at this point that he has done illegal things in the past: "It was as though he knew very well that in Lombard's past actions legality had not always been a sine qua non" (chapter 1). It is pretty obvious he is not willing to discuss his affairs with Vera.
Therefore, after she asks him about the Owens, he wonders what to answer: "Lombard thought: Awkward, this—am I supposed to have met them or not?" (page 18). So he casually diverts Vera's attention by pointing out she has a wasp crawling up her arm (a lie, most likely). This changes the subject of the conversation to wasps and the heat, going back to the initial weather topic, as it usually happens in casual talks between strangers.