The latest book in Alexander McCall Smith's popular 44 Scotland Street series is a sheer delight.   Summer has come to Scotland Street. The long days have prompted its denizens to engage in flights of fancy. Some, like the Duke of Johannesburg&;s plan to create a microlite seaplane, are literal flights, and some, like the vain Bruce Anderson&;s idea of settling down with one of his many admirers, are more metaphorical. With the domineering Irene off pursuing academic challenges, Stuart and Bertie are free to indulge in summer fun. Stuart reconnects with an old acquaintance over refreshing peppermint tea while Bertie takes his friend Ranald Braveheart Macpherson to the circus. But their trip to the big top becomes rather more than the pleasant diversion they were hoping for. Once again, Scotland Street teems with the daily triumphs and challenges of those who call it home, and provides a warm, wise, and witty chronicle of the affairs in this corner of the world.   AN ANCHOR BOOKS ORIGINAL