"There was an eerie silence. I stepped round a group of people and saw a man pointing a gun at a nurse."
What happened next is why Sgt Stevie Bull will be standing in front of some of the most famous people in the country when she collects her Pride of Britain Award on Monday.
The 28-year-old was nominated by her colleagues after tackling and disarming a gunman at a London hospital.
Stevie will be presented with the This Morning's Emergency Services award.
The Pride of Britain Awards celebrate British people who have acted bravely or extraordinarily in challenging situations.
Sgt Bull - who was a PC at the time but has been promoted since the incident - was at University College Hospital in London on a routine call when she realised something serious was going on.
"I saw people looking down a corridor and then looking at me. I thought, 'This is something I need to get involved in'."
She was alone though, with hospital security having gone in the wrong direction.
To make it worse there was a large suitcase near the man. Stevie was worried it could have been a bomb.
"We're trained to run away from firearms because I was an unarmed officer.
"I was so close to him that it was fight or flight mode and I just went for him.
"I screamed something at him. Then I just launched myself at him."
Stevie was nominated for the award after she tackled the man to the ground.
"I didn't think about my own personal safety. I just acted on instinct.
"I tried to get the firearm off him and he didn't want to let go so we had quite a roll around down the corridor."
Stevie pinned the man to the floor and, now with the help of some security officers, handcuffed and detained the suspect until her colleagues arrived.
It later turned out that the gun was a starter pistol - a gun used to start events and races that usually fires blanks.
Stevie was treated for injuries to her neck and head after the struggle but wasn't seriously hurt.
She says the awards ceremony on Monday night is going to be "very different" to a normal day, when she'd be doing a late shift in east London.
The ceremony is usually attended by members of the royal family, the prime minister and in the past footballers like David Beckham have also handed out awards.
"It's a lot of attention. A lot of my team didn't know I'd been nominated for the award. I've kept it very quiet," Stevie says.
"I think it's positive that I've won this award because sometimes I just want to hide under a rock - but actually, I'm very touched."
The Daily Mirror's Pride of Britain Awards will be broadcast on ITV on 5 November at 8pm GMT.