Complex sentence: His first story "Time Trap" (1948) is unusual for a first story in that it shows many of his recurring themes, among them art, time travel and a hero undergoing a quasi-transcendental experience.
Split into simpler sentences: His first story "Time Trap" is unusual for a first story in that it shows many of his recurring themes. Among these are time travel and a hero undergoing a quasi-transcendental experience.