A man walking the streets of a town with a running chainsaw and a mask sparked a major armed police operation.
Concerned residents dialled 999 after spotting the man walking along Churchill Road, Bicester, Oxfordshire.
Armed police arrived but found that the man, whose chainsaw had no blade, was going to a fancy dress party as horror film character Jason.
He was warned that he had to turn the saw off but allowed to continue to the party.
A Thames Valley Police spokesman said: "He was warned about his actions and told he faced arrest or a fixed penalty notice if he did not turn the saw off.
"It looks like he was in fancy dress but it was not a funny incident for worried residents."
The film character Jason is best known from the Friday the 13th horror films.