In Amsterdam Tim stakes out and films Barbara whose car killed agent Salinger. But the film he brings home is not his: It shows the accident. Trying to check with Barbara he finds murdered American Cordwell in her apartment.
For inspector Trueman both Barbara and Tim are suspects in the murders. He checks the contacts Salinger had on the day he died. When Tim returns home two men are ransacking his apartment and knock him out.
When Tim checks out the cafe 'The Dyke' a grocer gives him unwanted tips for the races. Returning at night Tim can't find the grocer, but in the cafe he meets Vivien, the business partner of Barbara. A catalog of tulip bulbs is a new lead.
Tim contacts the shady Dempsey and realizes that his tulip business is a front for the covert operations of the mysterious Ericson. Barbara's fiance, Arthur, is pestered by the police and ask Tim for advice.
The fake grocer contacts Tim and promises to tell him the truth but is shot to death before he is able to do so. Tim contacts Dempsey again and persuades him to meet in the park at night. Before Tim arrives Dempsey is viciously attacked.
Lewis from the office provides Tim with fake diamonds that Tim wants to sell to Ericson. Vivien offers a vital clue and orders him to come to a remote, empty house. No police, of course. When Tim arrives he makes a gruesome discovery.
