Der Hexer (1964)
Entertaining krimi based on an Edgar Wallace novel (The Ringer) that had already been filmed multiple times, going back to the silent days. Starts with a secretary overhearing something her boss is saying on the phone. She is then strangled. We cut to her body inside a tiny submarine, and the otherwise black-and-white movie turns into psychedelic color, as we get a rock 'n' roll song mixed with screams, moans, and the sounds of guns being fired over the opening credits.
That's quite a beginning. The woman knew too much about a white slavery ring, and also happened to be the sister of a notorious vigilante called DER HEXER ("the magician," in the English subtitles) who drove criminals to suicide, and is now in Australia. His wife arrives in England, and it's obvious that he's snuck in as well, ready to avenge the murder of his sister.
This leads to a three-way cat-and-mouse game, as the cops try to catch the white slavers and DER HEXER, while the white slavers try to kill the inspector on the case and evade DER HEXER, and DER HEXER kills the white slavers one by one (although they also do some of the work for him themselves) while evading the cops.
There's a guy from Australia claiming to be a writer who's following DER HEXER's wife, there's a kleptomaniac turned butler to the leader of the white slavers, there's the inspector's girlfriend, the inspector's boss and his sexy secretary, and a retired inspector who is the only person around who can identify DER HEXER, who is also a master of disguise. Lots of killings and attempted killings, chases, a multiple twist ending, and some comedy relief that is actually pretty amusing. An enjoyable romp, overall.