Two teenage girls were surrounded and attacked at a train station in Angus, police said.
One of the victims had been attacked outside the building in Arbroath, before both made their way to platform two.
They were then encircled by a group of young people and the second victim was punched and kicked. Both suffered bruising.
A woman saw the incident and pulled the two girls away from the crowd and onto a waiting train.
It was the 12.59pm service to Edinburgh at platform one, on Friday June 21.
Officers are aiming to identify three suspects - all are girls and white.
The first is described as 15 years old with ginger hair in a messy bun.
She was wearing a puffy jacket that is reported to have been red in colour.
The second is described as having a large build, ginger hair in a half ponytail and wearing a black fleece and black leggings.
The third is described as having a slim build with long dark hair, 15 years old and wearing baggy blue jeans and a black jacket.