Complex sentence: The Soviet defector Oleg Gordievsky divulged a top secret KGB telegram sent to the London KGB residency in February 1983 which listed seven "immediate" and thirteen "prospective" tasks for the agents to complete and report.
Split into simpler sentences: The Soviet defector Oleg Gordievsky divulged a top secret KGB telegram sent to the London KGB residency in February 1983. An attachment listed seven "immediate" and thirteen "prospective" tasks for the agents to complete and report.