Baden-Württemberg detectives have kept details of the incident, which happened in July, secret - so they could conduct investigations without alerting the kidnappers.
The victim fell in love with a woman via internet contact during the summer, police said, and travelled by train from his home in the Ortenau district, to Spaichingen, also in Baden-Württemberg, to meet her.
But police said that when she picked him up and took him home, he was met not by romance but by violence – two men were waiting for him.
They beat him and, together with the woman, forced him to clean two filthy flats.
The kidnapper trio then beat him again and left him to sleep naked in a corner on the floor, detectives said.
The following day they took him to Tuttlingen where they forced him to buy them a mobile phone and laptop before taking him to a bridge where they dangled him head-first off the edge, threatening to drop him.
He was only released on the third day, left traumatised and requiring hospital treatment for his injuries.
The police are still trying to work out why the suspects dreamed up the idea to get themselves a slave. A spokesman said all three were without work or anything sensible to do all day.
“They used the days to amuse themselves with various senseless things,” he said.