Mr Satterthwaite has accepted an invitation to stay at the house in the country of a couple called Denham. He is uncertain as to why he has done so as they do not part of the usual circles that he inhabits. John Denham is in his forties and his wife, Anna, is a refugee from the Russian revolution. Arriving at their house, he is told that the couple are out but expected back soon and Mr Satterthwaite passes the time by going for a walk in the garden from where he progresses to a lane which borders the grounds called "Harlequin's Lane". He is not surprised to meet Quin there who he finds is also staying with the Denhams. They walk down the lane, known locally as the "Lover's Lane" to its termination which is a former quarry which is now a rubbish tip. Returning to the house they meet a young girl in the lane called Molly Stanwell who is also staying in the house. She tells them that the Denhams have returned, they having been at rehearsals for a local masquerade that night, part of which is an enactment of the Commedia dell'arte for which two professional dancers are coming down from London to play the parts of Harlequin and Columbine.
At dinner that night the conversation turns to the soviet state and the tragic murder of the ballerina Kharsanova by the Bolsheviks in the earliest days of the revolution. After dinner a phone call is received to say that the two dancers for the masquerade have been injured on their way to the house in a car crash. The car was being driven by another Russian called Prince Sergius Oranoff who arrives later on and Satterthwaite wonders whether he and Anna are in any way romantically linked but he is amazed afterwards, while taking another walk, that the lovers in the lane are in fact John Denham and Molly Stanwell. Someone else has seen the couple though – Anna herself.
The masquerade takes place with Anna playing the part of Columbine while Quin is in the role of Harlequin. The performance is a success, so much so that Satterthwaite recognises by her dancing Anna is in fact Kharsanova and did not die but was rescued by John Denham when he was in Russia at the end of the First World War. In the darkness of the garden, she tells Satterthwaite that she gave up dancing at John's insistence but tonight she has found herself again and intends to elope with Prince Oranoff and then she moves off. Later on, he sees Anna and a figure dressed as Harlequin in the "Lover's Lane" but it appears to Satterthwaite that the man under the costume is John Denham. Soon after Prince Oranoff is looking for Anna and her maid says that she saw her in the lane alone. Satterthwaite is afraid for her and he and the prince rush down to the tip where they find Anna's dead body. Quin turns up and Satterthwaite asks why the maid couldn't see the figure of Harlequin. Satterthwaite can see things other people cannot, Quin tell him. Satterthwaite starts to say something to Quin, but the other is already gone.