As carefully noted in his scholarly postscript, the present book is in fact a translation of only about half (31 out of 65 chapters) of a Chinese book in Van Gulik's possession, entitled "Four great strange cases of Empress Wu's reign". Van Gulik obtained three editions of that book – a 19th-century manuscript and two printed editions, published respectively in 1903 and in 1947 at Shanghai. There were many differences between variant texts, Van Gulik considering the 19th Century version the best and basing his translation mainly on it.