How does Winter Garden end?

Winter Garden was written by Beryl Bainbridge. The novel is about a group of four English tourists named Douglas, Nina, Enid, and Bernard who visit Russia together. Douglas, a lawyer who usually lives a mundane lifestyle, initially sees the trip as a way to make his life more interesting and engaging. However, the trip turns out to be a nightmare for him. He becomes very uncomfortable with his surroundings, and the disappearance of Nina, his lover, under suspicious circumstances, makes him question whether people and events going on around him are real or a fantasy.
At the end of the story, Douglas is in a messy predicament. He is being detained because he is suspected of being a spy. As a foreign visitor to Russia, Douglas is worried about his possible punishment. He simply wishes he was at home with his wife instead of on the trip. At this point in the story, Douglas has still not been able to get in touch with Nina, who was also married and having an affair with Douglas. Douglas perceives himself and Nina to be at a standstill in time and space in a country that feels cold and remote, like a winter garden, as the title suggests. Bainbridge makes readers accept the complexities of life and realize that life is full of contradictions at the end of the novel.
The ending part of the story is also confusing. Events are left unexplained. At the end of the story, there are no explanations given for the disappearance of Douglas's luggage or the disappearance of Nina. Mysteriously, the location of Nina is never definitively determined, even though Douglas believes he sees her briefly on multiple occasions in different places. She is just missing for most of the novel. Additionally, Douglas's luggage is eventually found and returned to him, but he sees it has been searched without explanation. Douglas is a lawyer, so all these illogical events torture his logical mind, as someone who has built his life around being a rational person. He is made irrational by unexpected and surprising turns of events.