Set in the Aegean in 1944, the Nazis have taken control of an island and are busy digging up archaeological artifacts to ship back to Germany. Well, some of them. The best stuff, the base commandant (Roger Moore) is sending to his sister.
One of the prisoners is a British archaeologist (David Niven) being used to oversee the dig, but he, an American POW (Richard Roundtree) who learned sleight-of-hand in the circus, and an Italian race car driver (Sonny Bono) have their own plans for a massive haul of gold plates hidden in a monastery on a mountain nearby.
In town, a Greek resistance leader (Telly Savalas) has his own plans to seize the Nazi's sub depot, with the aid of intelligence his brothel owner girlfriend (Claudia Cardinale) and her girls get from the soldiers. Into all this drop a couple of USO performers, a comedian and a swimmer (Elliot Gould and Steffanie Powers, respectively), who seem to know more than they should and are playing all sides.
I gotta tell you, I got progressively more excited watching the opening credits and seeing this bizarre cast list. Shaft's in this movie?! Sonny Bono! What the hell?! And it does not disappoint. Things start happening quickly, and then keep happening. Savalas is playing cat-and-mouse with a Nazi trying to track the coded transmissions he's sending and receiving from the Allies.
That culminates in an assassination attempt that isn't a convincing accident. The movie uses that to good effect to keep the tension on. Niven, Roundtree and Bono manage to take over the prison camp fairly early, but there's still the SS guys planning to kill a bunch of civilians as reprisals for the guy Savalas killed. So you get the preparations for that and subsequent battle, which turns into a motorcycle chase through a bunch of narrow streets and alleys.
(Some of the action is impossible, given one of the motorcycles has a sidecar and would not fit through some of the spaces, but Rule of Cool says let it slide, baby.)
Concurrent with that is the taking of the sub depot, which ends up having extra complications, right as Savalas is leading a small group up to the monastery. Roundtree, Gould and Bono are after the gold; Savalas has his own interests.
Moore gets to play charming, but in a vaguely pathetic manner, as Powers tends to play on his affections for better grub, then rebuff his advances. The SS guy, a major like Moore, is there to contrast as being a real shitbag, instead of just a slimy art thief. Roundtree gets to be alternately cool and serious. I think Savalas is trying for a man who buries his guilt at the sacrifices he's asking of others for the war, but I'm not sure he pulls it off. His being gruff and short with Gould or the other opportunists works, because he sees what he's doing as more important than grabbing wealth, but even with Cardinale, who is helping him, he seems too harsh.
Gould gets to be the glib fast-talker he always seems to be, but in a role perfectly-suited for it. His skill at driving a motorcycle doesn't make much sense. Especially when they say Bono's character was a racecar driver, then never have him show it off (he seems to be there primarily for comic relief.) Given how easily Gould's character seems to take to shooting people, I was never entirely sure if he and Powers knew what they were getting into from the start, or were just excellent opportunists. We're shown Savalas certainly suspects they aren't what they claim, but I'm not sure we get a definitive answer.