A teenage student chased a burglar down the street with an umbrella after he was tied up and threatened with a knife.
George Zelonka was revising for his A-levels in his bedroom when the masked intruder burst into his home in Hampstead, north London.
He forced the 19-year-old to the ground, secured his hands with cable ties and threatened to kill him.
"I was working in my room when out of nowhere my door sprang open and a guy in a mask with a knife came towards me," Mr Zelonka said.
"He got me onto the floor and said 'don't move, don't move, I'll kill you'.
"He put cable ties around my hands, I felt very helpless.
"I didn't know what to do, it was such a shock.
"I heard him unravelling a plastic bag and thought - I'm about to be suffocated."
Mr Zelonka managed to break free and screamed at his assailant: "You've no idea who you're f****** with".
He chased the burglar out of the house and down the street.
"He ran out the door, I saw an umbrella and grabbed it and chased after him," he added.
"It went so quickly, it was over in a flash."
He continued: "I'm quite traumatised and a little bit paranoid at the moment.
"I'm totally grateful that I'm all right and got out with just scratches on my wrists."
His dad Paul Goldstein said: "I was probably even more traumatised than he was, if anyone touches your children you feel very protective.
"I don't know what this guy's intentions were or what he was doing, I just hope he gets caught.
"George is not involved in any gang culture or drug culture, he's just quietly getting on with life."
The man was dressed in all black, with a hood, mask and gloves. It is not known how he gained entry to the house.
A Met Police spokesman said: "There were no reports of any persons injured at the address and the suspect, who reportedly had a knife, fled the scene with nothing.
"The suspect is described as Eastern Asian in appearance and wearing dark clothing. He ran off northbound towards Hampstead Heath."
Anyone with information about the incident, which took place at 5.45pm on Tuesday, should call Camden CID on 101.