South African director Gavin Hood's military thriller Eye in the Sky is frequently exciting, sporadically dull and ultimately invaluable. The big names, Helen Mirren and the late Alan Rickman, deliver their goods—unselfconscious power on her side, and bilious melancholy on his.It's a wider film than the similarly themed Good Kill. Hood shows us the war on terror as a literal world war, being strategized everywhere from the dust to the heavens.Yet Eye in the Sky truly belongs to Barkhad Abdi (Captain Phillips). Abdi is the anti-terrorist coalition's point man, Jama, who keeps surveillance on a heavily guarded compound on the outskirts of Nairobi. This spy pilots an insect-sized gadget, a flying, beetle-shaped drone camera. He poses as a peddler distracting himself with a thumb-operated cell-phone game, while selling buckets at an open-air bazaar. Abdi—a thoughtful, bemused actor—delivers during the tensest moments in this film. The varied military personnel on the coalition are merely risking their careers and their consciences. Jama is the one with his life on the line.In a tin-roofed house just a few hundred yards from the marketplace where Jama spends his days hiding in plain sight, there is a secret meeting of al-Shabaab operatives—all guarded by militia men wielding truck-mounted machine guns. Two of the attendees are wanted by both the U.S. and British governments. One is an American citizen. The other an English national."Operation Egret," the mission to capture the deviant duo, is the brainchild of the British Colonel Powell (Mirren), who has been chasing them for six years. At bases as far apart as Pearl Harbor and London, observers wait to view the terrorists' capture by local military authorities.That's when images reveal that the fanatics are preparing to strike again, immediately. At an airbase near Las Vegas, manned by a rookie airman played by Aaron Paul, observers prepare to trigger a Hellfire missile. The "kill chain" begins. In London's Whitehall, Rickman's Lt. General Benson persuades high-ranking yet timid government officials to consent to the execution of a British citizen. Amusingly, the dithering intelligence group is called "COBRA."What stalls the flight of a drone-born missile is the presence of a potential collateral victim, visible to the many watchers of the situation. There's a little red-robed girl (Aisha Takow) sitting by the wall of the targeted home, selling loaves of bread on a market's table. Her decision to stay or go is halting the kill-chain.Hood sets up this drone strike as if it were Star Trek's "Kobayashi Maru" test. "There is no law covering a situation like this," says Mirren's Powell. And there is no ingeniously correct action that prevents the killing of bystanders, either through a surprise missile strike or through inaction.White haired and splendidly uniformed in olive and crimson, Rickman has the final word during his last scene on screen. It's a memorable parting shot about the mistake of telling a soldier that he hasn't seen the cost of war. For one last time, we can take in Rickman's weight and menace, his baleful sensitivity, and the entropic quality of slow words, chilled down to absolute zero.But, too often, Eye in the Sky boils down to scenes of soldiers looking at computer screens in their bunkers. Hood persuades, and is himself persuaded, of the occasional necessity of these drone strikes. He shows us a letter-perfect and thoroughly vetted missile launch, studied from all angles. The top politicians may be slightly ludicrous—a Home Secretary, toilet-bound with food poisoning in Singapore, a beefy American Secretary of State, busy playing ping pong with the Chinese delegation. But they do their jobs, and they're on hand to rule on a state-sanctioned killing.When the hypotheticals are stacked this high, a viewer has no way out except to agree. It's like watching an episode of 24, where the terrorists' hands couldn't be redder. The argument that is impossible to accept—even after seeing the brimming eyes of actors playing the soldiers—is that their tears have an equal value to the blood of innocents.