In less than 100 pages, this invaluable book by Nyanatiloka Thera, an eminent German shcolar-monk, provides a superb synopsis of the Dhamma and is said to be probably the best compact source book in English on the Buddha's basic teachings. It provides an outline of the Buddha's teachings directly in the words of the Pāli Canon, the oldest authentic record. Said to be first published in 1906, it has since been translated into several languages.
This book is published by the Buddhist Publication Society (BPS). Also, the Paperback could be purchased from BPS, should you wish to do so (www.bps.lk).