A man who thought he was opening the door to a trick-or-treater had acid thrown in his face by an attacker dressed as a ghost.
The victim, thought to be in his 30s, opened the door on Halloween in High Wycombe at around 7.45pm
Police say the offender threw two cups of pink liquid over the man wearing a Halloween costume.
He was rushed to hospital with burns to his face and feet.
A Thames Valley Police spokesman said: He answered the door and there was someone dressed as a ghost, in a white sheet with eye holes cut out.
The victim assumed the person was a trick-or-treater for Halloween, but the offender then threw two cups of liquid over the victim.
The liquid was pink in colour, and has been confirmed as high strength corrosive substance.
The victim sustained burns to his face and feet and was treated at Wycombe General Hospital but has since been discharged.
Detective Sergeant David Mitchell said: This is a worrying attack involving a liquid, which has been established by our colleagues at Buckinghamshire Fire and Rescue Service as a high-strength corrosive substance.