The letter which the main character Mrs Drover finds in her abandoned London family home appears to be from her long-lost soldier-lover. The letter-writer reminds her that this day is their anniversary and that he will be coming for her.
The letter is short and is signed only 'K', but Mrs Drover seems to be left in no doubt as to who has sent it. She is perturbed by it as she remembers her soldier-lover as being an unpleasant, controlling character; moreover, he was presumed dead in World War I.
Equally troubling is the question of how the letter has arrived in the empty house. There is a caretaker who looks in every now and then, but Mrs Drover believes him to be on holiday and even if he has returned, she is surprised that he would leave the letter in this fashion as he always forwards the Drovers' mail to their new home in the country. It does not seem likely, then, that the caretaker could have left it.
Therefore the appearance of the letter is a strange occurrence and Mrs Drover is fearful that the letter-writer could have broken into the house. So she escapes outside - only to be seemingly abducted by a taxi-driver. We are not expressly told that this is her 'demon lover' come to take her away, but certainly it seems to be someone who means her harm, 'accelerating without mercy' and steering her away from normal life into some dark and isolated domain - 'the hinterland of deserted streets'.