Complex sentence: Control was convinced that one of the top-level officers in the Circus was a Soviet mole, and believed that a Czech General, disillusioned after the crushing of the Prague Spring, had offered to reveal the mole's identity.
Split into simpler sentences: Control was convinced that one of the top-level officers in the Circus was a Soviet mole. Control believed that a Czech General, disillusioned after the crushing of the Prague Spring, had offered to reveal the mole's identity.