At the end of the second book Light was preparing himself to live under surveillance, and volume three finds Shinimagmi `Death God', Ryuk floating through the walls and ceiling identifying where all the hidden cameras and microphones are. Knowing that he is being carefully observed Light works hard at trying to look inconspicuous - but he also has to maintain his Kira killings otherwise he will invite further suspicion.
This volume contains less action than the previous volumes, there seems to be less focus around the detail of the killings. Instead there's more emphasis on the battle between L and Light, and it's a relationship which takes an interesting turn when the two meet for the first time. The main strength of the Death Note story is the interplay and rivalry between them and this volume represents the best of their war-of-wits so far.
Ryuk's role this time round is quite different. There's no need for Ryuk to explain how the Death Note works now as the rules are well established. He provides the odd moment of humour here, especially when he sulks over a lack of apples and expresses how tired he is after searching for cameras. Ryuk seems to be sitting back and enjoying the show, he is very intrigued and amused by Light's use of the Death Note. We also get to see more of the Shinigami world, it's only a brief part of the book but it gives a good idea of how individual they are, and their attitudes towards humans.
In a nutshell: Another strong book in the Death Note Manga series. The plot develops further, but more importantly the relationship between Light and L advances to another level when the two start interacting directly with each other.