A man suspects his girlfriend of being unfaithful, so he sends her a letter, but then finds out that he was wrong. He has 24 hours to stop the package, prevent a disaster, and fall in love. The only problem is the delivery man will not stop until the package has been delivered.

When World War I breaks out, brothers Roy and Monte Rutledge, each attending Oxford university, enlist with the Royal Flying Corps.

Dave is convinced that his knock-out girlfriend Jamie is cheating on him, despite his best friend Victoria's reassurance that it's all in his head. When his life begins to unravel, both at work as well as in his relationship, Dave's suspicions overwhelm him and he stumbles upon a discovery that turns his world upside down. After following Jamie to a "study group" one night, Dave is shocked to learn that his girlfriend is the leader of a conspiratorial group of ex girlfriends, whose sole purpose is to torment him and ruin his life. Following the discovery, Dave finds himself tumbling through a series of adventures as he attempts to unveil the truth, all while getting his life back on track. With the guidance of several questionable comrades, and the help of the conspirators' alluring new but reluctant recruit Katie, Dave ultimately pieces the puzzle together and finds out the hard way that sometimes true love is worth fighting for.

A complex series of events transpires after a paranoid guy snoops on his girlfriend's phone and sees that she has been texting with someone else.