It's April 1944, and moody Walter Hoffmann of SD Intelligence (now more powerful than the Abwehr) has been entrusted by Himmler with the war's most important mission: Germany must get its hands on someone who knows the location and date of the impending Allied invasion of Europe. So Hoffmann applies pressure on canny Jurgen Brausch of the Abwehr, an anti-Hitler sort who has a precious agent in Britain: handsome Gus Lang, a.k.a. ""Emerald,"" an OSS man who's a double-agent working for the Nazis. Will Gus give the Germans helpful information? Yes he will--even though he's really a triple agent, truly loyal to the USA! And, through some UK/US spy bungling, Gus' information turns out to be too helpful: the Nazis do indeed sink a US ship on a test-run to France, capturing Andy Wheeler, a timid radio whiz who knows the Normandy-invasion secret. Somehow, then, the Allies must silence or save Wheeler before the Germans torture those secrets out of him. Luckily, the Nazis summon ""Emerald"" to Paris, where the Wheeler interrogation is beginning: they want Gus to pose as a POW, share Wheeler's cell, and win his trust. So, while pretending to work for the Nazis, Gus really spends his cell-time slyly coaching Wheeler to feed the Germans a phony invasion plan. But eventually, of course, the very smart, essentially decent Hoffmann grows increasingly suspicious of Gus--leading to showdowns, a bit of violence. . . and ultimate escape for Wheeler, Gus, and super-beautiful Claire (Gus' new French Resistance love), Lacking the taut simplicity of Eye of the Needle, this D-Day-secret scenario teems with implausibilities: the dubious ease of Gus' impersonation, the unlikely behavior of the top Nazis, excess convolutions involving another double-agent. And the Gus/Claire romance, complete with Claire's adorable wee daughter, tends to wallow in cuteness and sentimentality. Still, the pace is quick, the narration is crisp, and there's some solid tension in the interrogation crisis; so fans of WW II spy-tangles should find this a serviceable diversion, with much steadier entertainment value than Bass' busy, routine debut, Lime's Crisis (1982).