As a little girl, Catherine wants to marry her firefighter dad. Her mom says, “You can’t marry Daddy, I’m married to him. ” The film relates what transpires 25 years later. Catherine is now married to young firefighter Caleb Holt (Cameron). On the job, Caleb lives by the motto “Never leave your partner behind”, forcefully impressing this dictum on the men in his fire crew. But his marriage with Catherine (Bethea) is suffering and she wants a divorce. Differing life priorities have led their marriage to a breakdown.
She complains that he is addicted to internet porn; she views his saving money for the boat of his dreams as selfish, believing the money should be used to provide her ailing mother’s medical equipment. Caleb feels respect from everyone except his own wife, who he says does not value him. Caleb’s father John challenges him to commit to a 40-day “Love Dare” (a real-life Christian devotional program designed to strengthen marriages, also written by the film’s writer, director and producer team of Alex and Stephen Kendrick. Caleb apprehensively agrees to try it, and begins following the program in an attempt to win Catherine back. But she doubts his sincerity, suspecting his real motive is just a ruse to obtain a better divorce settlement. She sees Caleb’s acts as half-hearted, like the inexpensive flowers he buys her. Caleb learns, though, to hold back from blowing up in anger or insulting Catherine to her face. Frustrated with her coldness, but with John’s encouragement, Caleb continues on the plan. His close friend Michael (Bevel) encourages Caleb to become a born-again Christian.
He illustrates the together-yet-different nature of a healthy marriage through salt and pepper shakers he has glued together. Caleb may try to pull them apart, but if he does, the contents will break one or both of them in the end. At the hospital where she works, Catherine begins flirting with the friendly Dr. Gavin Keller (Perry Revell), and tells him of her mother’s medical problems. Meanwhile, Caleb injures his arm in a firefight, and is brought to the hospital. A nurse inadvertently says (in front of Dr. Keller) that Caleb is Catherine’s husband.
Continuing his 40-day challenge, Caleb begins doing more household chores and errands. He leaves her more expensive beautiful roses, and even smashes his computer to remove its temptations. But Catherine still thinks he has an ulterior motive, and she remains intent on divorce. Catherine learns that a new wheelchair and bed for her mother have been paid for in full. Assuming that Dr. Keller bought the wheelchair, she arranges a lunch date to thank him. Meanwhile Caleb discovers Dr. Keller’s budding relationship with Catherine, and warns him he will not let Catherine go without a fight.
Dr. Keller begins to distance himself from Catherine. He tries on his wedding ring, but it no longer fits. One morning Catherine is home sick, and Caleb decides to take care of her. She asks why he has changed his behavior, and he tells her about the Love Dare and apologizes for his past selfishness. Catherine says she needs some time to think about their future. A few days later, she learns it was Caleb, not Dr. Keller, who paid for the lion’s share of her mother’s new medical equipment, exhausting his long-term boat savings.
Finally she sees that Caleb’s desire to change is sincere. Ashamed of doubting him, she dons her own wedding ring, dresses and makes herself up, and rushes to embrace her husband with the respect and admiration he has craved. When Caleb thanks his dad for the Love Dare, he is surprised to learn it was his mother who first did the Love Dare on John, not the other way around. The young couple renew their wedding vows in an outdoor ceremony, this time as a covenant with God. The closing shot shows their wedding cake, with salt and pepper shakers for its bride and groom statues.