Complex sentence: The book is the first of a trilogy, including "Darkness at Noon" (1940), and "Arrival and Departure" (1943) on idealism going wrong, a common theme in Koestler's work and life.
Split into simpler sentences: The book is the first of a trilogy, including "Darkness at Noon" (1940), and "Arrival and Departure" (1943), which address idealism going wrong. This is a common theme in Koestler's work and life.