Alamut (Bartol Novel)
en.wikipedia.org
en.wikipedia.org
Hassan-i Sabbah's militant group was known for taking drugs (hashish) as well as the targeted murdering (assassinations) of key figures during the Crusades. So they were referred to as hashishins (arabic for hashish-smokers) which was eventually turned into assassins and thats where the term comes from.
The only thing I'll say is if you've read that Assassin's Creed is "based" on Alamut, you might be a bit disappointed. I would say it's more of a "heavy influence".
Still, it is one of those books, you’ll select almost as random as a teenager in your local library and it stays with you.
Interesting. Never heard of this book or author.