He said Henry was leaving a bar in Courtney Pl in the early hours of Friday morning when he got into an argument with a man he didn't know. The man took the verbal argument a step too far and pulled a knife on the 23-year-old.
Soper said Henry put his arm up to fend off the blow. But the knife went through his forearm, slicing nerves, tendons and damaging an artery.
Bleeding heavily, Henry was taken to hospital. The offender ran off but Police arrested the man.
Soper said his son, a "feisty bugger", had only got back from six months in Melbourne the day before and was celebrating with friends.
It is not certain whether Henry, who is working in events management with his mother, will get the full range of motion back into his arm.
Soper agreed with his wife Heather du Plessis-Allan, who penned an opinion piece about the incident being caused not by alcohol, but by violence. He said his daughters, who live in Melbourne, had spent the weekend lecturing him on the dangers of the streets.
"I've had many arguments in my life but I never expected someone to pull a knife on me.
"I have always felt very safe in New Zealand. I'm shocked that somebody would be armed on the street. I guess that shock is a little naive.
"In Melbourne you've got to be very careful. Clearly you've got to be careful in New Zealand as well."
Soper, who called his son a "very likeable young man", thought the attack may make him more reserved in the future. The surgeon had told them it would be a long process to get back to normal. In the meantime Henry was being inundated with visits from friends bearing gifts of chocolates and flowers.
"He's got a great sense of humour. He's bearing up as best as he can."
A 37-year-old man was arrested and has been charged with wounding with intent to injure. He appeared in Wellington District Court on July 29 where he was remanded in custody.
He will appear in court again on July 31.
