Police say it is pure luck no one has been injured or killed in a string of suspicious fires at the Foxton racecourse.
There have been four fires at the course in the last 10 days, including one which extensively damaged the grandstand and another which burned down a stable building.
The latest fire was spotted shortly after it was started at 4.45am on Sunday. Only minor damage was caused to the caretaker's shed door before it was put out.
Acting Detective Sergeant Marianne Whitfield says someone with a serious issue with the club seems to be behind the fires.
She says it is vital that anyone with information about the blazes contacts the police immediately.