A 60-year-old man is in a critical condition in hospital after a row on a bus in County Durham, police said.
The victim was on the 243 Arriva service from Hartlepool to Horden when he became involved in an argument with two men and a woman on Saturday night.
The men ran at him as he attempted to leave the bus and seconds later he was unconscious on the pavement with a serious head injury.
Durham Police are now trying to establish how he was hurt.
The victim was trying to get off the vehicle with his 41-year-old partner in Beech Terrace, at the top of Horden Bank, when the incident happened.
He was taken to Sunderland Royal Hospital and then transferred to Newcastle General Hospital.
Det Sgt Cliff Down said: "It is unclear how the victim sustained his life-threatening injuries.
"Establishing the exact sequence of events will be part of our investigation.
"We particularly want to speak to two elderly ladies who got off the bus at Blackhall."