A baby was raised by wolves and when he looked to be about 8, he was captured and put on display in a traveling show as 'the Wolf Boy'. Well, this kid (dubbed 'Etoile') continued the act for sometime...even though he had become civilized and a nice guy. Then, suddenly and for no reason I can think of, one day he goes berserk, turns into a wolf-man and kills someone--all after being with the show many years.
On the run, Etoile makes his way to Paris where he gets a job working at the zoo....all because of his natural affinity with animals. He soon falls for a prostitute but is naive enough to think she's just some nice lady. When he catches her with a john (after all, this IS her job), he goes berserk again...turning into a wolf-man and savaging the guy. He later does the same to other johns who frequent this lady. There is no full moon involved...and it seems that when Etoile gets upset he becomes a human-animal hybrid.
Investigating the case is a very intelligent professor (Peter Cushing). He uses modern investigative techniques to determine what is going on...though the dopey police seem to hold little of what he says to heart. Can this professor sort all this out and help the police stop this menace? Or, can he somehow manage to cure Etoile of this weird malady?
Let's cut to the chase. There have been quite a few werewolf films before this and most of them are simply better. This one just doesn't make a lot of sense and it ignores the wolfman canon. It also isn't as entertaining and atmospheric as many of these other films. Worth seeing...but far from a must-see horror flick.