Today, there are still secrets that need stealing, and the consequences of detection remain dangerous. Moscow's recent expulsion of an alleged CIA officer was dramatic, but such moves are among the lesser costs of espionage gone awry.

How, then, does a case officer persuade someone to become a traitor? There is no definitive handbook. The process is as complex as human relationships. If possible, a friendship should develop between the case officer and the prospective agent; bonds of trust must be established. But beneath the surface, there is the CIA officer's constant and often uncharitable assessment of the target's aspirations, fears and desires. You must know what motivates the potential recruit so that you can better exploit his vulnerabilities and, in the end, put him in the right frame of mind for your 'pitch.'

In making this assessment, the CIA relies on four basic human motivations, described by the acronym MICE: money, ideology, conscience and ego. Some agencies in the U.S. intelligence community, perhaps not realizing that MICE is already a plural word, insist on adding an S to the end for sex. But sexual entrapment is not a reliable recruitment technique. A blackmailed agent tends to be resentful, brooding, prone to disloyalty and the fabrication of intelligence. Other countries, most infamously Russia, have used sexual entrapment in intelligence operations without compunction.

The relationship with an agent motivated by money is straightforward: 'We give you cash, and you steal secrets.' Consider the case of the aircraft mechanic in a North African country who, in 1974, reported that six new export models of the Soviet MiG 23 fighter had been delivered to his military air base. He was willing to photograph every detail of the planes and proposed being paid per frame, as long as the images were of value.

One night, under a brilliant African moon, he crawled all over the plane, snapping photos. For a final rear-facing shot, he shinnied out onto the shark's nose of the aircraft─and suddenly slid backward off the front. He looked up to discover that he had bent down the hollow nose needle at a twenty-degree angle. Unable to straighten the thing out─and worried that his payment would be jeopardized─he proceeded down the flight line in a panic and bent the five needles on the remaining fighters to match the first. He got his money, but his access was lost, along with his usefulness.

The agent motivated by ideology─or, as often as not, by the traumatic loss of ideology─may develop slowly, sometimes over years. This agent no longer believes in her government. She has been abused by the system and hates the superiors who have ruined her career. Lots of regimes around the world, past and present, take away hope and institutionalize despair: Stalin in the 1950s, the mullahs in Tehran in 2013. A Soviet military officer named Dmitri Polyakov, posted to New York in the 1960s, was refused permission by an implacable Moscow to take his fatally ill son to a U.S. doctor. His ideology faded, his heart hardened and he started to work with the CIA. He is still considered one of the agency's best assets ever.

The agent motivated by conscience bears watching. He may be messianic and looking for ways to atone for his sins, or for the sins of his system─or for all the Evil in the World. The ticking of remorseful conscience may come with age, with too much war or betrayal, or with having driven a tank in Tiananmen Square. Or it may come with enlightenment. Perhaps an Iranian nuclear scientist─rational, humanistic, a man of erudition─will realize one day what it would mean for the Islamic Republic to have nuclear weapons and will emerge from the subterranean centrifuge halls of the Iranian desert with secrets in hand.

The agent motivated by ego is a blessing and a curse. Properly stroked, he can be responsive, motivated and focused. But once the stroking starts, you cannot stop: He will be needy, moody, demanding. Ego is one of the most powerful human motivators, and it encompasses sex, as the Russians knew very well in running their sexual ambushes against targets inside and outside Russia over the years.

A case officer also looks for prospects among individuals who seem to be in search of an ego, their spirits stamped flat by purges, cultural revolutions or protracted tax investigations (a favorite tactic of today's Kremlin). In the late 70s, one agent with abysmal self-esteem and a nervous disposition was told (falsely) by his case officer that his intel tidbits had been reported to the White House to rave reviews. His shriveled ego flowered: He now had people who counted on him and admired him! That's all it took for the meek little man to ignore his fears and begin bringing out classified documents─all in the belief that he was personally spying for Jimmy Carter, God help him.

The spy game is a perfect subject for examining the human condition. Its practitioners traffic in trust and betrayal, hope and fear, love and hatred. And even now, our intelligence needs multiply─in the rush to understand how Russia will use natural gas to extend its reach, or how soon Iran will have a nuke, or how Beijing plans to achieve hegemony in the Pacific. Case officers around the world continue their work, trying to persuade people to become traitors and deploying tools as old as the trade itself.