Dead Watch, by John Sandford, is a standalone. The author writes two series, the Prey books (some of which I have read and can definitely recommend if you like the police procedural/thriller mix genre); and the Kidd series, which I haven't read.
Dead Watch is very good for the first two-thirds. A retired senator has vanished, and soon is found dead. Was he abducted by the Watchmen, a cross between the boy's brigade and a private police force of the state governor? Or is there a more complex conspiracy in play? Jake Winter, a US Army veteran who is a political insider and spare-time university academic, is called in by the White House — not only to investigate the case but also to distance the president from any possible fallout. The best parts of the book concern the Washington insider politics, and Jake's dance with the various political factions, the grieving widow (or is she?), the media, and a group of the dead man's friends — I particularly liked the way that nobody did anything until they had worked out all their future deniability options. The less good part is at the end — as is so often the case with thrillers — when the inevitable action finale takes over. Dead Watch will certainly pass the time on a journey, though.