Donna Leon’s The Jewels of Paradise (Heinemann, £17.99)has a promising premise. A young musicologist, Caterina Pelligroni, returns to Venice to trace a legacy left by the 17th-century composer Agostino Steffani, a slippery customer who mixed libretti with realpolitik in the courts of Europe. The bequest turns out to consist mainly of nasty secrets, which seem strangely important to the attractive yet shady lawyer who has hired Caterina.