Having finished Sea of Tranquility by Emily St. John Mandel I moved straight onto the book's companion The Glass Hotel. Where Sea of Tranquility is definitely a science fiction novel with more literary elements, The Glass Hotel does not present itself as an SF&F novel. True, there are some paranormal elements towards the end of the book, one character in prison spends their time thinking about parallel realities and the final part of the book is set in 2029 but each of these elements retains a sense of the story being set in our world and in our reality.
The story follows a Canadian woman with the unusual name of Vincent, from the death of her mother when Vincent was a teenager to Vincent's own death many years later. In both cases, they die by drowning at sea without witnesses. While Vincent connects the sections of the narrative together, the novel follows other characters around her including her brother who aspires to be a composer but struggles with addiction, and her future not-exactly-husband, a financier whose elaborate Ponzi scheme unravels during the 2008 financial crisis.
It is very well written and I enjoyed it. It looks in various ways at the compromises people make with their own personal morality with various characters making choices at various scales of moral dubiousness. The Ponzi scheme as an agent of fate and as a symbol of historical events around 2008 is a clever choice. Once started, there is an inevitable doom just waiting to happen to such schemes. In the end they must unravel and when they do multiple people will suffer.
The book is literary fiction and as I already said, has a few touches which touch on the borders of SF&F. There is a broader theme of people moving between world metaphorically but the section set technically in the future is there to show characters we have met later in their lives reflecting on events, i.e. in the future but not futuristic.
However, it is worth looking at the genre aspects of the story because it is overtly a companion piece to Sea of Tranquility. Vincent and her death are also events in Sea of Tranquility, her brother's eventual success as a composer is also a key plot point in the novel and an unusual experience Vincent had in her youth is part of the central mystery of Sea of Tranquility. That experience does not appear in The Glass Hotel and additionally, a major character in one book has a very different fate in Sea of Tranquility. Yet that different fate is one that the same character dwells upon as a might-have-been in The Glass Hotel.
The two books together have a shared narrative of which Vincent is a key component. Sea of Tranquility features Mirella, a former friend of Vincent whose husband killed himself as a consequence of the Ponzi scheme featured in The Glass Hotel. You can read the two books independently of each other, but Mirella's desire to know what became of Vincent leads to her learning of her mysterious death at sea. In Sea of Tranquility, this feels like an unresolved plot point of the broader story about time travel and a mysterious anomaly that connects Vincent with characters in multiple time periods.
Put another way, if you read both books together, the science fictional elements of the second intrude into the first. The time traveller Gaspery-Jacques is told in the 24th century that he is just one of several people being sent back in time to interview people connected to the anomaly, suggesting that any number of incidental characters in The Glass Hotel may be time travellers. The differences in how some common events play out between the books also highlight Sea of Tranquility's theme of parallel worlds and the simulation hypothesis.
Mandel plays games with her other books of course. The apocalyptic Georgia Flu from Station Eleven is mentioned as a minor health scare in The Glass Hotel but the connections with Sea of Tranquility are deeper than these kinds of Easter Eggs.
So if The Glass Hotel isn't SF&F (and it isn't) and Sea of Tranquility is (which it unambiguously is) then what are the pair of books together as a combined narrative? Notably, both novels have been announced as future television adaptations by HBO and I wonder how they will be produced and marketed? Will they be interlaced as one bigger weirder story or pitched to audiences with different sensibilities but with overlapping characters?
Of course The Glass Hotel repeatedly has characters talking about entering new social situations as if they are transported to a new country almost in the way of a portal fantasy, Vincent in particular living three very different lives (sequentially though rather than in parallel). That the characters then can also shift genres is only fitting and fits neatly with the metaphor of the first book and science fiction premise of the second.