Love defines us. It shapes the individual, ensures the preservation of the species, and is the principal subject we - as a culture - choose to examine in our art forms. The experience of being in love is powerful and it inevitably changes how we feel and how we behave. Even when love is normal it is so intense that for thousands of years doctors and poets have described love as a kind of madness; however, love can also go wrong. When this happens the consequences for the individual and those around them can be far reaching and in some instances truly astonishing. Lovesickness is not a trivial matter. Unrequited love is a frequent cause of suicide (particularly among the young) and over ten percent of murders are connected with sexual jealousy. In the course of his career, Frank Tallis has treated many fascinating patients, and their stories, told here, are dramatic, bizarre and revealing.