It’s been a summer where the law of diminishing returns continues to apply and such is the case with director James Mangold’s “Night and Day.” Here is a movie that stars Tom Cruise and Cameron Diaz and gets off to a high flying start, only to glide on action and star charisma the rest of the way. It’s pleasant and entertaining, but it’s also another movie that doesn’t try too hard.

Cruise is secret agent Roy Miller and Diaz is June, two people thrown together during a flight between Wichita and Boston. Miller is attacked, which begins a long chase where the FBI, led by Fitzgerald (Peter Sarsgaard), think Roy has gone rogue, Roy thinks Fitzgerald is the real bad-guy, and June is caught in the middle. “Knight” is much like “The Bounty Hunter” and “Killers,”with one exception; it’s watchable.

Cruise is in Ethan Hunt-mode, jumping from car hood to car hood and building to building, crash-landing planes, dodging bullets, airplane-bombers, and explosions, and narrowly escaping during a car chase in Spain. All the while he has this wild lunacy and cool-under-pressure demeanor that shows us he’s having a blast, and we’re going right along with him.

And Diaz makes for a freaked-out but feisty accomplice.

Jennifer Aniston and Gerard Butler should take note, Cruise and Diaz are funny, likable and fun together, and the exotic locales just add to the easy, breezy feel.

It’s too bad all the fun loses steam during “Knights” middle-section, right before the exciting finale. Other flaws could have been corrected too. Roy’s goodness or badness is predictable before the flick even starts, Patrick O’Neill’s screenplay lacks scenes that really sizzle, and you can tell some of the action scenes were done with CGI. There is also a running gag involving sedation that as comedy works but as actioncomes off lazy and dull.

Still, “Night” is easygoing enough to enjoy, if not totally love.