Six people were taken to hospital after an accident on the A706 near Forth on Friday.
Three of them remain in hospital with serious injuries.
Now Police Scotland is appealing for witnesses.
The accident happened about 4.20pm, when a black Peugeot 206 travelling southbound on the A706 collided with a red Citroen C1 car and then hit a white Ford Fiesta, causing it to come off the road and go down an embankment.
Emergency services attended and occupants of all three vehicles were taken to hospital.
The male occupants of the Peugeot 206 were taken to Wishaw General Hospital. Two men, aged 19 and 22 remain in hospital with serious injuries. A 15-year-old was later released from hospital with a shoulder injury.
The 25-year-old male occupant of the Ford Fiesta was taken to the Queen Elizabeth University Hospital and is in a serious condition.
The occupants of the Citroen car, a woman aged 22 and a child aged 4, were conveyed to Wishaw General Hospital as precautionary measure but were later released.
The road was closed for several hours as crash scene investigators conducted enquiries at the location.
Officers are appealing for any motorists who may have been on the A706 around the time of the collision taking place. Anyone with any information or dash cam footage is asked to contact Road Policing officers at Motherwell Police Station via 101, quoting incident number 3874 of Friday September 1.