My all-time favourite introductory book on Buddhism is Buddhism: A Very Short Introduction by Damien Keown. It combines scholarship, brevity, clarity and personal experience into a perfect introductory package.
There is a companion to this book, also from Oxford University Press and also by Damien Keown, called Buddhist Ethics: A Very Short Introduction.
I haven’t read all 148 pages yet, but the few I have read are exceptional. Keown discusses the precepts and the monastic Vinaya, the Buddhist response to war and terrorism, sexuality, abortion and suicide and euthenasia.
All these subjects are treated sensitively and in a balanced way. For instance, Keown doesn’t shy away from the instance in history where Buddhist countries have been involved in war – he also asks whether there is such a thing as a just war – or indeed the Dalai Lama’s response to the gay community about whether gay sex is in accordance with the Vinaya.