Daughter Of The Crocodile

It's 279 BC and Ptolemy Philandelphus finds his wife ousted by his reptilian sister, who wants to marry him herself. A generation later, and Berenike Beta murders her husband and marries Ptolemy Euergetes instead. But with the glory of the Ptolemies at its height after Egypt wins victories at Syria, it is the turn of the murderess to be murdered.