IANAL and off-topic, but if it was a series title, your friend might have a case but, at least in North America, the titles of single works are generally not pr

IANAL and off-topic, but if it was a series title, your friend might have a case but, at least in North America, the titles of single works are generally not protectable under trademark law. If the book became strongly associated with your friend, then a consumer protection exemption under "Passing Off" rules might allow the work to be protected but the onus would be on your friend to prove it.