NOTE: This spoiler sent in by Frugalwife.
This starts with Caleb, the fire captain, (Kirk Cameron) chewing out a trainee at the fire station for leaving his partner behind during a house fire. Caleb was most emphatic, you NEVER leave your partner behind.
It then shows him going home and how horrible his married life is now. He argues with his wife Catherine, over money and how chores are divided (he does none). She fires back with his time on the computer, not family friendly web sites, and how he has saved $24,000 for his boat, not a common goal. It comes out that her parents need her help since her mother had a stroke. You can tell this marriage is on life support.
At work, there is a call for a rescue unit involving a car accident. It is a badly damaged car with two teenage girls trapped in it. One is unconscious, the other begs for help. Caleb promises to not let go of her. The car is on a train track. He calls for the dispatch to stop all trains in the area, but they are not able to do so. There is a crowd of people and they call out that there is a train coming. There is a look of sheer panic as they try to push/lift the car out of the way of the train, as there is no time to hook up a chain to pull it. Some of the men in the crowd come to help and they literally get the car out of the way just in the nick of time. One of the firemen's helmet is knocked of by the train and a soldier what helped lift the car out of the way, holds onto him as the train passes within inches of him. This is Caleb's close friend and he asks Caleb to not tell his wife how close this brush with death was for him.
Caleb goes home and has a huge fight with his wife, who tells him she wants out. Caleb accuses her of being disrespectful to him, you can tell this means a lot to him. This happens several times.
He goes out in the yard and hits the trash cans, then realizes the neighbor is watching him.
Caleb calls his father who tells him he will come in the next day to see him. His dad does and tells him that he needs Jesus in his life and Caleb disagrees, but agrees to hold off on the divorce for 40 days. His dad promises to send him a package. The next day, Caleb gets a hand written book from his father called the Love Dare. It starts off easy, with the first day of saying nothing bad about your spouse. You can tell Caleb is only doing this to please his father and does it minimally at best. He gets some really cheap flowers for his wife, makes her coffee and when she doesn't want it, pours it in the sink and leaves the mess for her to clean up. Catherine works at a hospital and there is Dr. Gavin who flirts with her regularly and tries to woo her away.
About halfway through the dare, Caleb is suppose to cook dinner for her. His friend at the station, advises him to go all out, best dishes, candles, music, good food, if he can't cook, buy it. Caleb does and Catherine tells him she doesn't love him at all. He calls his dad and his dad says he will come to visit him the next day. He and his Dad walk through a park area and his dad tells him this is the hardest part and the reason he isn't doing well is that he is a sinner and needs the forgiveness that Christ offers if he asks. Caleb does admit this and becomes a Christian. One of the first things he does is to tell his friend at work. His friend is always encouraging him to try hard and to stay married.
There is a fire where a little girl is still in the wood frame house, when her father realizes this he tries to run in, but is tackled by fireman. Caleb goes in, with all of the proper gear, and is separated by falling boards. He finds the little girl and chops through the hardwood floor to under the home. He crawls out and the other firemen pull the girl out then him. He is sent to the hospital that his wife works at, and the doctor that has been treating him is the one who flirts with his wife! The next day, Caleb has had two phone calls for interviews, but his wife doesn't want him. He starts looking at boats on the internet, and a website pops up, for a pretty girl that says wanna look? He fights this, then take the computer monitor and hits it with the baseball bat. He looks up and his neighbor is watching him. (Funny) He does the same with the computer and when Catherine gets home, there are a dozen red roses where the computer was with a note, I love you more. She leaves him a note, that he sees in the morning, and they are divorce papers. He is very upset. In the mean time, Catherine goes to the medical supply store, where she had priced a bed and wheelchair for her mother, only to find out that someone donated the money for it. She is very happy and thinks it is Dr. Gavin. She thanks him profusely and they flirt together.
Caleb then is cleaning the house when he finds a card that Dr. Gavin wrote to his wife flirting with her. He goes to the hospital and gets in the doctor's face showing him his wedding ring and makes a fist in the doctor's face. When Caleb leaves, the doctor opens his desk drawer and takes out HIS wedding ring, but decides not to wear it. Dr. Gavin quits eating and spending time with Catherine.
Catherine gets sick and for the first time ever, Caleb takes care of her without her asking. He gets medicine for her and brings her soup. She has found his Love Dare book that his father wrote for him. They talk without fighting and she is very uncertain of his reasons. He explains he is now a Christian and that is the difference. She is reluctant to try. A few days later she goes to the medical supply store to get more sheets for the bed for her mother, when she tells the lady she knows Dr. Gavin gave the money, but the lady corrects her and tells her it was her husband, who gave the money, $24,300. She walks out without the sheets, goes home and gets her wedding ring and goes to the fire station to meet Caleb, and tells him he is a good man and she wants to grow old with him. They kiss. Later they are walking at the same park where Caleb and his father did, and Catherine becomes a Christian as well.
Then his parents come for a visit and the dad explains to Caleb that he didn't write the book, he copied it. It was his wife's book that she used to win his heart back two years earlier and that he was the one that wanted a divorce. Caleb had been unfair to his mom and apologized.
The movie ends with them retaking their vows as Christians.