The agency has been hired by an actress called Tasha Mayo who is being stalked by one of two brothers in their forties who closely resemble each other.  Barclay has dubbed them ‘the Frankenstein brothers’ due to their unusually high foreheads; this is abbreviated to Frank One and Frank Two.  In Chapter 13 we find Robin and Barclay watching the block of flats in Bexleyheath in which the brothers live.

The brothers are described as being fairly shabbily dressed. Robin tells Strike ‘Frank One’s got a bit of a squint and Frank Two’s balder’ (Chapter 17).

Barclay discovers that it is both of the Franks that are stalking Tasha Mayo, not just one of them. This is bad news for the agency as it means they now need double the manpower to watch them. Strike watches the Franks donning disguises and purchasing a worrying selection of objects from a Sports Direct shop some distance from their home (Chapter 32) which leads him to believe they are going to make a move on Tasha.

When they do make their move, the agency is ready, and the case is resolved to the satisfaction of the client.