When Jan Servaas, a world famous Dutch violinist, makes a rare concert appearance in his home country it is an eagerly awaited event. In the weeks leading up to the concert van der Valk receives a series of mysterious notes, written on blue paper, warning that Servaas will be ""executed"" if he comes to Amsterdam. Van der Valk ignores Kroon's pleas to have the concert canceled until the case is solved, perhaps in part because he and Arlette have tickets and are looking forward to it! It is a decision that will have tragic consequences as a drama which began with betrayal in wartime Limburg plays out to a fatal conclusion in 1970s Amsterdam.

Officers investigating a hearse abandoned near the Royal Palace make a bizarre discovery which appears to be a threat against Paul Harkemer, well known editor of a right wing magazine, and/or his 19 year old daughter. At first it appears that it may be nothing more than a publicity stunt for the left wing rock band Emerald Scorpion, and Harkemer himself seems totally unconcerned. The case seems to over before it started, but then the police receive a cassette tape from someone claiming to be the kidnapper of Harkemer's daughter.

A body dredged up from a canal is tentatively identified as the son of a British MP, but when she views the body she says it is not her son. Van der Valk refuses to believe this and calls on his British colleagues to help prove the boy's identity. The boy's face is well known in Amsterdam's transvestite and transexual scene and van der Valk's inquiries there lead him deeper and deeper into a dark world of sexual depravity and exploitation involving some of the most prominent public figures in Europe. Samson of course desperately advises him to proceed with extreme caution. In the face of the mother's refusal to co-operate van der Valk finds his best hope is to look elsewhere in the family for help.