More than 300 people in France have reported being pricked out of the blue with needles at nightclubs or concerts in recent months.
Although doctors and multiple prosecutors are on the case, no one knows who's doing it or why, and whether the victims have been injected with drugs – or indeed any substance at all.
People from Paris, Toulouse, Nantes, Nancy, Rennes and other cities around France have reported being pricked with a needle without their knowledge or permission.
The targeted individuals, who are mostly women, show visible marks of injection, often bruises, and report symptoms like feeling groggy.
Club owners and police are trying to raise awareness, and a rapper even interrupted his recent show to warn concert-goers about the risk of surprise needle attacks.
The problem is not isolated to France.
The UK government is studying a spate of "needle spiking" there, and police in Belgium and the Netherlands are investigating scattered cases too.
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On 4 May, 18-year-old Tomas Laux attended a rap concert in Lille in northern France, where he smoked some marijuana and drank some alcohol during the show.
When he came home, he said he felt dizzy and had a headache – and he spotted a little skin puncture on his arm and a bruise.
The next morning, the symptoms didn't disappear and Mr Laux went to a doctor and later A&E, where medics confirmed evidence of a needle prick.
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He was tested for HIV and hepatitis and his results came out negative, like other victims' so far.
"I've given up going to concerts since it happened," Mr Laux said.
The French national police agency has said 302 people have filed formal complaints about such needle pricks.
Several police investigations are ongoing in different regions, but no suspect has been arrested yet, no needle has been found and the motive remains unclear.
In the UK, parliament issued a report in April on drink and needle spiking in pubs and nightclubs after a surge in such incidents last year.
It said police reported about 1,000 cases of needle injection across the country around October 2021, when students returned to campuses after COVID restrictions eased.
However, the parliament report said there was a lack of data to judge how serious the issue is.
It's not clear whether anyone has been prosecuted for needle spiking, or how many victims were injected with a drug or other substance.
As investigations continue with no perpetrators found in France, rapper Dinos interrupted his concert in Strasbourg this week and said: "This has to stop."