This book really is the bridge to the Empire novels, part of the Foundation series. It is not a detective novel, and it concentrates on the Robots, Daneel and Giskard, and their relevance to the Empire, as well as Earthmen and Spacers. Baley has died by this point, and Daneel, as well as Giskard, who revealed at the end of the last book that he had the power to influence minds, [Asimov explains the scientific basis behind this, realists may be glad to discover!] have to protect the Empire. Unfortunately the First Law of Robotics continually holds them back. All throughout the book Daneel toys with this law, and eventually comes up with a solution - the Zeroth Law of Robotics. This book is an essential read. It is not as entertaining as previous books, but is crucial to understanding the Empire novels.
'Scintillating and stimulating'