Three good Samaritans were injured on Brighton seafront when they stepped in to try to stop a gang beating up a man.
Two of the victims were stabbed. One was stabbed in the throat and the other suffered a wound to the hand.
The third victim suffered a head injury after he was hit with a weapon.
Sussex Police said: “The victims were on their way home after a night out when they found a man on the mid level of Madeira Terrace being assaulted by a group of males at about 4.40am on Saturday 5 October.
“They intervened and the 20-year-olds were themselves attacked sustaining serious injuries.”
The friends ran off towards the Palace Pier. They were chased by the thugs but were caught outside the Harvester restaurant in Marine Parade where the attack continued.
Detective Constable Paul Ash said: “This was a brutal attack that has left the victims with potentially life-changing injuries.
“They were incredibly brave to step forward to help a stranger.
“There would have been a lot of people in the area at the time and I desperately want to speak to anyone who saw the incident or heard what happened as the violence spread from Madeira Terrace to Marine Parade.
“I would also encourage the man who was initially being assaulted by the offenders to contact us.”
The first offender was white, 18 to 20 years old and at least 6ft tall. He had a muscular build and short dark hair and was wearing a t-shirt which he tore during the attack. He had a tattoo on his upper chest.
The second offender was white, 17 or 18 years old, small and skinny. He had cropped hair.
The third offender was white, pale, about 18 years old and 5ft 9in tall. He had shaggy black hair and was wearing a t-shirt.
The fourth offender was white, 30 to 40 years old and had very short hair or was bald.
Anyone with information is asked to call Sussex Police on 101 or the independent charity Crimestoppers anonymously on 0800 555111.