What an engrossing, scary, complex and excellently crafted literary work! I think that LeCarre' is simply a great English writer posing as a thriller master.
The plot seemed a bit (to me) as if it's a re-work of "The Spy Who Came in from the Cold", post the threat of Russia and the Cold War, current the threat of rogue devils, roaming the world selling arms, drugs and misery (such as "now"). The "most evil man in the world" has a scheme to pedal stolen arms to thugs for drugs, which can them be marketed in Europe and America.
Our hero, (a former operative for the forces of good) now retired early to a job as night manager of a swank hotel, has a horrible history with this evil man. The evil one, and his entourage including a lovely girl, checks into the swank hotel one snowy night. Slowly the action begins to unfold.
A "skunk works" intelligence operation in London, engaged in it's own war with "pure intelligence" forces of the empire (could be another novel), proceeds in secret to transform "night manager" into a
criminal who can eventually be planted with the evil doers to bring them down. (This takes about half the novel, but is interesting.) Similar to the process in Spy/Cold.
The writing craft makes the novel: visionary, horrifying without being too graphic, funny.
The love story is a little lame; my only criticism. "Jonathan Pine" is an interesting character,
the girl is not. In the book, she was rather similar to Taylor Swift, in appearance. The girl, though beautiful, is not substantial enough for someone as complex as Pine.
I did not bother to watch the mini-series based on the book. Most often the movie based on any book is disappointing if you liked the book.