Half of all new marriages end in divorce but scientists say they've found the secret of long lasting love. They claim they've identified how love works and can even tell which marriages will make it. If so, can they save couples whose relationships are on the brink of collapse? Lyn and Alan have bickered for 21 years and are contemplating divorce. Hayley and Jay have been married for seven years, but Jay's recent affair has put their marriage under intolerable pressure. Along with starry-eyed newly weds, Steve and Donna, our warring couples go through a battery of experiments to see what's going wrong. We find out whether being out of love affects how we physically see our partner, and in one of the most daunting stress tests known to psychologists, how our physiological reactions to conflict threaten love. Armed with new understanding of each other's biochemical and psychological behaviour, Lyn and Alan, Hayley and Jay embark on a programme designed to rescue their relationships.