Loosely based on the gruesome case of the Lonely Hearts Killers, who murdered as many as 20 women in the 1940s, Alleluia is not for the faint-hearted.

75岁的皮耶自从太太过世后就过着孤单的生活。女儿帮他买了一台电脑，想着也许能提起爸爸的好奇心，甚至替他找到第二春。皮耶跟着年轻的电脑老师亚力克斯学习上网，意外发现一个交友网站。他借用亚力克斯的身分，认识了帐号Flora63的年轻物理治疗师。皮耶对她着迷不已，Flora63也深受这位高雅不凡的人士吸引