The Peshawar Lancers - S.M. Stirling
This was a bookswap book, by a writer I hadn't previously heard of, taken pretty much on the basis of the blurb.

It's an alternate history tale, where Victorian London (and significant parts of the northern hemisphere) are struck by meteors that leave desolation in their wake, forcing a mass emigration south. The Empire still exists, but its heart is in India, not London, and the ruling families have taken Indian culture and religion on board, amalgamating them seamlessly into their former way of life.

Our protagonists are brother and sister: Athelstane King, officer of the eponymous Peshawar Lancers, and Dr Cassandra King, eminent physicist. Attempts are made on both their lives, throwing them into esteemed company as Cassandra finds herself employed as a tutor to the Emperor's daughter, while Athelstane and his sidekick try to track down the source of the threat to themselves and the Empire.

In general, The Peshawar Lancers is an entertaining read, although Stirling does suffer badly from the 'my loads of research, let me show you it!' problem, leading to serious info-dumps at times. It's clear he has done his research, particularly into the culture of his setting, but it does start to get a little tedious at times when the reader is regularly reminded of how thorough the author has been in this regard. I'm not sure I'd actively seek out Stirling's other alternate history books, but I wouldn't hesitate to pick one up if I came across it, so that must say something!