A 22-year-old man was robbed at knifepoint as he a travelled on a train near Drumchapel station in Glasgow.
The robbery happened at about 23:00 on Thursday after the Whifflet to Dalmuir service left Westerton station.
The victim and a friend were approached by a man who produced a knife and demanded an iPhone from them.
The robber then got off the train at Drumchapel. Detectives have described him as a white man in his 20s, about 5ft 10in tall and of slim build.
He had dirty blonde hair and a scar on his right cheek. He was wearing a two-tone grey tracksuit with a large EA7 motif on it and was carrying a bottle of Buckfast.
British Transport Police believe the armed robber and another man may have been in the Anniesland area before the incident.
They have appealed for witnesses or anyone with information to contact them.