A man is in a critical condition in hospital after being attacked at a car wash in Falkirk.
Central Scotland Police said the 49-year-old suffered a serious head injury after being assaulted at the Arc car wash in New Carron at about 0815 BST.
The force are investigating reports that the man, who was driving a red Fiat, had been involved in an earlier incident on the M9 motorway.
They said the 21-year-old driver of a green Volkswagen was being questioned.
The 49-year-old man was taken to the Western General in Edinburgh following the incident.
Det Ch Insp Willie Cravens said: "The 21-year-old was driving a green Volkswagen Golf and the 49-year-old was driving a red Fiat people carrier-style car.
"They were both heading west and left the motorway for Falkirk and continued to the car wash where the assault occurred.
"We appeal for anyone who may have been travelling on the M9 around 8am and who may have seen the two cars."
Mr Craven said the force was keen to speak to anyone who saw either of the cars travelling from the motorway to New Carron between 0800 BST and 0815 BST.