But when he turned the handle nothing happened.

‘Waterloo was 1815, you dunce,’ said Cam, as he pushed past Dabs and Jane to enter the right code.

‘Sorry, I was listening to Tchaikovsky’s 1812 Overture while I was driving to work this morning.’

‘You like classical music then?’ Jane asked.

‘Yes, very much. I quite often go to concerts at the Royal Albert Hall.’

‘It soothes the savage beast in him.’

Cam smirked as he shoved the door open and entered the building. He made no effort to hold the door open, and as it was on a hinged spring, it would have hit Jane if Dabs hadn’t put his hand out just in time.

‘Where’s your manners, Cam?’ Dabs said, as he held the door open for her.

Cam mumbled an apology, said he needed a ‘Jimmy Riddle’ and turned left to go down the concrete and worn green lino-covered stairs to the basement toilets.

The hallway and stairwell walls were painted a puke green, which couldn’t disguise the patches of mould, and a damp smell filled the air. Jane was a bit surprised to find the interior of the building was in a worse condition than any police station she’d worked in before.

‘Sorry about Cam – he can be a right surly git at times. He gets frustrated at not being involved in the investigative side of things. Mind you, he is a good driver.’

‘You don’t need to apologise for Cam’s behaviour. If he wants to be an investigator he should apply to become a detective and stop moaning.’

Dabs put his hand on Jane’s arm.

‘Mind you don’t slip on that wet patch. We’ve got a leaky roof, which was supposed to have been repaired weeks ago, and some of the stairs to the top floor are a bit wet as well. The cleaner does her best to keep on top of it, but she can’t predict the rain unfortunately.’

‘Was this building ever a working police station?’

‘No, it used to be an office block with a woodwork factory on this floor where they made doors. The company went bust and the building lay empty until the Met bought it specifically for the Flying Squad a few years ago. As you can see, it needs some repair work and a lick of paint, but it’s much better upstairs in the squad office.’

‘Who uses the downstairs?’

‘The surveillance team – though one section of it is used as a lock-up for the exhibits we seize during our investigations.’

‘What – like guns and ammunition?’

‘Yes, among other things. They go up to the firearms unit lab first for examination and when they’ve finished with them we store them here.’

‘The building doesn’t look very secure,’ Jane said, having seen the outside in the morning.