The first thing you should know about Joe and Gertie Stein is that they lived in a enormous dark house with cobwebs in the corners and bats in the roof space.
The second thing you should know is that they were both ordinary children with parents who made them eat sprouts and sent them to bed at the same time every night.
And the third thing you should know is that when you live in a house the size of a castle there’s a world of difference between being sent to bed and actually going.
Night after night Mr and Mrs Stein would sit watching the television in the downstairs livingroom, blissfully unaware that instead of drifting off to sleep in the third-floor bedroom, their children were running wild through the house.
Through ringing cellars, up narrow spiral staircases leading to high turrets, across vast attics, Gertie and Joe scampered, with knapsacks on their backs and torches in their hands.
And their parents knew nothing of it.
‘Why do my children always have bags under their eyes?’ Mrs Stein asked one night. She folded her newspaper and looked inquiringly at her husband.
9.30pm THURSDAY
Mr Stein got up to adjust the television set.
‘Perhaps they don’t get enough sleep,’ he said. ‘We’ll start sending them to bed half an hour earlier. This telly’s playing up a bit, I think we’re in for a storm.’
Meanwhile, upstairs in the third-floor bedroom, Gertie was stuffing a spare jumper into her knapsack and checking the batteries in her torch.
‘Where shall we go tonight?’ she asked.
Joe was looking out of the window. ‘It’s beginning to rain,’ he said. ‘That means the cellar will be flooded and the attics will be leaking.’
‘Which leaves us the turrets, the west wing or the labs,’ said Gertie.
‘Not the labs,’ said Joe. ‘Not in the dark.’
Gertie and Joe’s parents were research biologists, which meant that they spent a lot of time tinkering about with test-tubes and squinting at computer screens. They both worked at home, so they had converted several rooms on the east side of the house into laboratories. They never kept anything really horrible in there, just a few gallons of blood on which they ‘ran tests’, but…
‘Not the labs!’ Joe repeated, in case Gertie hadn’t got the message.
‘It’s only blood,’ said Gertie tetchily, ‘It can’t throw itself out of the test-tube at you.’ She thought a moment. ‘I know, let’s go to the west wing, we haven’t been there for ages.’ And she switched on her torch with a practised flick of her thumb.