I aim to startle as well as please," Muriel Spark has said, and in these eight marvelous ghost stories she manages to do both to the highest degree. As with all matters in the hands of Dame Muriel her spooks are entirely original. A ghost in her pantheon can be plaintive or a bit vengeful, or perhaps may not even be aware of being a ghost at all. One in fact is the ghost of a man who isn't even dead yet. Another takes the bus home from work, believing...