Mr Satterthwaite is at the Royal Opera House in Covent Garden. Not caring for Cavalleria Rusticana, he deliberately arrives late so as to see only Pagliacci. He arrives, in fact, just before the interval when he bumps into Mr Quin. He invites Quin to watch the second opera with him in his private box from where they spot an absolutely beautiful-looking girl in the stalls before the lights go down. In the next interval they spot the girl sat with an earnest-looking young man and see that they are joined by a third young man whose arrival appears to have generated some tension in the group.
At the end of the evening Satterthwaite offers Quin a lift home but the invitation is politely declined and so Satterthwaite is making his own way to where his chauffeur-driven car is parked when he again sees the three people from the Opera House. Almost immediately a fight breaks out between the two young men and Satterthwaite rescues the girl from the fracas and he suggests that he drive her home. She accepts and he takes her to Chelsea. She tells him her name is Gillian West, the intense man is Philip Eastney and the other is Mr Burns and she hopes that Eastney hasn't hurt Burns. Satterthwaite promises to find out and assuage her fears.
The next Sunday, Satterthwaite is in Kew Gardens when his path again crosses that of Gillian West and Charlie Burns and he finds that the two have just become engaged. Gillian is nervous of the effect that the news will have on Philip Eastney and Charlie confides that men previously have lost their heads over his fiancé and done stupid things as a result. The next Thursday, Satterthwaite goes back to Chelsea at Gillian's invitation and has tea with her. To her relief, Eastney has accepted the news with good grace and given her two wedding presents. One is a new radio and the other is an unusual glass sculpture which is topped off by a bubble-like iridescent ball. Eastney has made a strange request – that Gillian stay at home tonight and listen to the broadcast of music on the radio.
Satterthwaite is uneasy as he leaves Gillian, feeling that the appearance of Quin at Covent Garden must mean that there is some unusual business afoot but he cannot place exactly what is going to happen. Wanting to discuss his fears with Quin, he goes to the Arlecchino restaurant where he met him once before when discussing the trial of Martin Wylde (see: The Sign in the Sky). Quin is not there but Eastney is and the two men talk with the younger man regaling Satterthwaite with his tales of working with the testing and manufacture of poison gas during the war.
Leaving the restaurant, Satterthwaite is still uneasy and eventually he buys a paper for that evening's radio programmes and realises out that Gillian West is in great danger. He rushes to her flat and drags her out before the tenor's voice reaches a peak during a performance of "The Shepherd's Song". A stray cat goes through the door to the flat and is found dead – killed by the gasses freed from the glass ball when it shattered as a result of the sound of the radio.
Satterthwaite meets Eastney who is pacing on the Chelsea Embankment and tells him that a dead cat was removed from the flat, i.e. that Eastney's plan failed. The two men part, and a few minutes later a policeman asks Satterthwaite if he also heard what seemed like the sound of a large splash, which both men agree would probably be what someone throwing himself from an embankment into the river would sound like.