Sabre-Tooth by Peter O'Donnell

Karz, a modern-day Genghis Khan, is assembling an army of mercenaries in a hidden valley in the Hindu Kush Mountains. His objective: the invasion and occupation of oil-rich Kuwait. But he lacks a couple of top lieutenants, and his gaze falls on Modesty Blaise and her loyal companion Willie Garvin, even though he knows they are not for hire.

Meanwhile, Sir Gerald Tarrant, who runs a secret service organisation under the British government, has noticed that many mercenaries are being recruited by some unknown employer and disappearing. This worries Sir Gerald, and he asks Modesty and Willie to investigate. When Karz kidnaps Lucille (a child dear to Modesty and Willie), and commands them to report for duty, the adventurers have no choice.