One man died and four others were injured in a collision involving three cars and a horse.
Emergency crews found a car on its side in a ditch, a second on its roof and the third, a taxi, with minor damage.
Two men suffered serious head injuries in the accident on the A452 Kenilworth to Leamington Spa road in Warwickshire. The horse was fatally injured.
Two people were treated at the scene and then released. The road has since reopened.
Police said that shortly before the accident, at 0030 GMT, they received reports that a horse was loose on the A452, near Chesford.
A green Rover 114 heading towards Kenilworth collided with the horse and overturned.
A blue London taxi, heading towards Leamington Spa, and a silver Citroen Saxo, travelling towards Kenilworth, were also involved in the crash.
A male back seat passenger in the Rover was thrown from the car, suffering head injuries. He was pronounced dead on arrival at hospital.
The male driver and front seat passenger have been taken to hospital with serious injuries.
An ambulance spokesman said crews had searched for more possible victims.
"There were reports of a fourth man in this vehicle so ambulance crews requested the police helicopter use its thermal imaging to search the area but no-one else was found," he said.
Police have now traced the horse's owner and are investigating how it came to be on the road.