A female train conductor was indecently assaulted on a journey from Derry to Belfast, police have said.
The incident happened on Saturday when the woman intervened after a group of male passengers became rowdy, the PSNI said.
The woman was allegedly grabbed by one of the men and verbally abused.
She was then grabbed by another man as the group left the train at Mossley West, the PSNI added.
A PSNI statement said: "The conductor was left extremely shaken and upset by the ordeal.
"It is appalling that a woman was subjected to such attacks while simply doing her job.
"We are investigating and would like to hear from witnesses."