The motives for being so recruited to serve another country vary. The recruit may be in debt, in a bitter marriage, passed over for promotion, revolted by his own regime, or simply lust for a new life and plenty of money. He may be recruited through his own weaknesses, sexual or homosexual, or simply by sweet talk and flattery.
Two things pricked me from the above passage -- 1) The use of 'he'. I know how it's a matter of style for a lot of writers to use 'he' or 'him' while they obviously mean both the genders. Forsyth doesn't particularly strike me as that kind of a writer because of his colossal attention to detail, especially when there were women defectors. Since thrillers/suspense are primarily aimed at men, it even makes sense for a young man to imagine a woman as a recruit for espionage. It adds spice. 2) Sexual or homosexual - Is homosexual not sexual? Such political incorrectness spotlights that he still thinks from a different age.