More than music is exchanged when the Corsicans come to St Griswolds to join the choir for their Christmas concert. Alongside the singers an incompetent but deadly terror gang is threatening anyone who performs Mozart. Flora, the soprano soloist, blames Mozart for her parents' death in a plane crash, and accidentally joins the gang. Her twin sister Dora has fallen for Max, the choirmaster, a secret agent, who is on the trail of the terrorists. Max's twin brother Mordred, the Cathedral organist, is hereditary Chairman of LEMUR, a secretive, unscrupulous and fabulously wealthy insurance company based in Corsica; the fortunes of several members of the choir are bound up with this mysterious organisation. With new technology providing immense challenges, the supremacy LEMUR has maintained for 500 years is about to be called to account.