Despite finding it a bit hard to start, I tremendously enjoyed Chris Beckett's Marcher novel -- I would recommend not reading the extract at the beginning of the book. The italicised prologue is a bit heavy too, but provides some context and once you get through it the story gets interesting already, following Charles, an immigration officer dealing with "shifters", people using a drug to move between the worlds, or more accurately alternative timeline our world could have taken. People who have enjoyed Beckett's short stories will recognise the world and happily notice echoes of other stories (I'd recommend reading The Turing Test first, even though you don't need to!).
There's a social comment thread of the story that can't be separated from the main plot, and sometimes doesn't feel so far from home. In this world the poor and unemployed are confined to special "inclusion zones" where they get a chance to "pull themselves together" and benefit from social welfare in the meantime, and as we explore these places and meet the social workers who work in them, we get to see the less-than-ideal reality of this social system's implementation. The tension begins when shifters start appearing in the inclusion zones and hiding there before committing horrible crimes, and shifting away before facing the consequences.
The book is littered with many distracting spelling mistakes, words doubled, "to" instead of "two" and so on. Grr. Bad editing job. Besides that annoyance, the story is fantastic, especially as it picks up when the strange crimes start happening and we follow some events from a shifter's point of view. I read in the bus and was starting to look forward to traffic jams to have more time to read, and eventually had to stay home and get to the resolution of all this! This is very entertaining science-fiction, combined with an interesting look at society.