Describe the encounter between Dahlia and Spode in Tom's study in Chapter 18.

Dahlia recounts being alone in the study with Spode after Tom leaves the room to take a telephone call. Dahlia tries to blackmail Spode, but he informs her that he no longer runs a women's underwear business. Dahlia discovers the cosh, which Bertie left in the study and hits Spode over the head. Dahlia takes the pearls, and when Spode regains consciousness, he believes he fell and bumped his head after an attack of vertigo.