Bartemaius tells the story of his previous association with Ptolemy set in 950 BC. Its an interesting story with themes similar to the Bartemaius trilogy and Stroud adds slavery to the issue at hand. 
 Its a light read and is enjoyable who liked djinn from the trilogy. His characterization remains pretty much the same and Ptolemy is reminiscent of Nathanial. (They aren't alike but its easy to draw similarities in certain plot points)