Me, Lex and Nicholas were hunkered down behind a car opposite Bianca’s house. We were on a stakeout. (The last time we did a stakeout, we made an amazing fake bin that all three of us squeezed into – but Bianca’s house was a last-minute stakeout so we didn’t have time to make a brilliant disguise. Besides, the amazing fake bin ended up being a magnet for yippy dogs and too small for us all to run in).

Bianca’s friend, Tara – who had also been on the Time Lords team for the scavenger hunt – was hanging out at Bianca’s house after school. At first they’d disappeared into the house, and we felt a bit silly hiding behind a car waiting for them to come back out, but now they were sitting on the wall of the front garden, checking their phones and chatting to each other.

Tara had a maroon mini-backpack on that she wore all the time. I remembered that she’d been wearing it the day of the scavenger hunt too.

‘If that backpack’s big enough to fit a weather vane,’ I whispered, ‘then the Time Lords had motive and opportunity.’

We weren’t trying to listen in on their conversation, but being so close we couldn’t help overhearing.

‘And I was like, I don’t care if you started wearing those bracelets first,’ Tara was saying, ‘cos like I’ve always liked them, and like I just wear them more. Like I’ve always had them.’

‘Oh my god,’ Bianca chimed in, ‘I know. Like I started wearing them a year ago.’

‘I never saw you wear them a year ago.’

‘I totally always wore them. Like not loads of them together, but like I’d always have one on.’

Tara checked her phone again. ‘Yeah, but loads of them is the thing. Like, we’ve all always had them, but Killian thinks he’s the first one. Like he always thinks he invented everything.’

‘Yeah, I know, like it’s so annoying.’

Lex leaned on me to peek over the car bonnet.

‘Do teenagers always talk like that?’ she whispered. ‘Are we going to end up talking like that when we go to secondary school?’

‘I’d rather eat my own arm,’ I replied.

‘This is so boring my brain’s going numb,’ Nicholas said, readjusting his feet. ‘And so are my legs.’

‘We just need to get to that backpack,’ I said. ‘If it’s wider than forty centimetres, then it was big enough to hide the weather vane.’

‘How are you going to check?’ said Nicholas. ‘Are you planning to mug her in broad daylight?’

‘No.’

‘Then what?’

I reached into my pocket and pulled out a measuring tape.

‘Are your pockets like Mary Poppins’ bag?’ said Nicholas. ‘Can you just pull anything out of them?’

‘It’s not magic, Nicholas,’ I said, looking down at him. ‘I’m just prepared. Like any brilliant detective should be.’

‘Well, brilliant detective, how are you planning to measure Tara’s backpack without her or Bianca noticing?’

That was a good question.

‘You two are going to have to distract them,’ I said.

‘How?’ said Lex.

‘You could have a fight. Yeah! A big shouty fight, and while they’re watching I’ll sneak up behind Tara and measure her backpack.’

‘Fight about what?’ said Lex.

‘I don’t know, anything. Just improvise.’

‘I can’t improvise. I’ll say the wrong thing.’

‘You can’t say the wrong thing,’ said Nicholas. ‘That’s what’s so great about improvising. You just go with the flow, say whatever you want – there are no wrong lines.’

‘I can’t.’ Lex was already looking scared. ‘I-I-I’ll say something wrong. I can’t make it look real.’

Nicholas sighed. ‘What if Cass and I have the fight, and you measure Tara’s bag?’

‘Okay.’

‘But what will we fight about?’ I asked, suddenly feeling like I was on the spot. ‘We need to decide.’

‘No we don’t,’ said Nicholas. ‘That’s what’s so great about improvising–’

‘We have to agree on something to fight about, Nicholas, otherwise it won’t look real.’

‘It doesn’t matter what you say, that’s the point. Just go with it.’

‘Oh really? Doesn’t matter at all? So if I said … I’m mad at you for wearing a frog as a hat, would that work? Can you improvise a fight about that, Nicholas?’

‘They’re coming this way!’ Lex suddenly hissed.

‘Nicholas, move!’ I snapped as Bianca and Tara crossed the road towards the car. ‘Crawl around to the back. Go, go!’

‘My legs are dead!’ Nicholas was trying to get out of sitting cross-legged without using his feet.

‘Move!’

I pushed on Lex, who tried to lift Nicholas, who knocked her into me; I tipped back and sprawled over the curb, right in front of the car.

‘Eh.’ Bianca stood over me with a weird look on her face. ‘What are you doing, Cass?’

Like a flash I zipped open a length of the measuring tape and pressed it to the road.

‘Checking for sinkholes.’

‘For what?’

‘Sinkholes. You know, sinkholes can appear anywhere at anytime. They’re these giant holes in the ground that just open up all of a sudden and swallow everything above them. I’m just, eh …’ I pretended to carefully read the measuring tape. ‘I’m just checking these cracks in the road. Checking they’re not getting bigger.’ I squinted up at Bianca and Tara. ‘Just making sure there isn’t a sinkhole on the way.’

Tara turned to Bianca. ‘The kids on your street are weird.’

‘You have no idea,’ said Bianca.

They were walking away when suddenly Nicholas popped up in front of them.

‘Ow!’ he yelled, suddenly grabbing his shin. ‘Ow, my leg! I think it’s broken.’

‘What?’ said Bianca. ‘How did you break your leg?’

‘Just there. Just now, when I fell. I think it’s definitely broken. Can you call my dad?’ He gestured to the phone in Tara’s hand.

‘Your house is right over there,’ Bianca said.

‘I can’t walk that far. Can you please call my dad? Please? The number’s O84 … no, wait … yeah, no, it’s 084, then I think 93 … no, wait …’

While Bianca and Tara were distracted by Nicholas, I crept up behind Tara and held the measuring tape to her backpack. Twenty-nine centimetres. Not wide enough to fit the weather vane. Over Tara’s shoulder I shook my head at Nicholas.

‘Actually,’ he said, standing straight, ‘I think it’s fine. Yeah, it’s actually fine. Must have been a cramp or something. Thanks anyway.’

Tara frowned at Bianca as the two of them walked away. ‘The kids on your street are seriously weird.’

‘Good work,’ I said to Nicholas, ‘but her bag’s not big enough.’

‘If the Time Lords didn’t take it,’ said Lex, ‘where did the weather vane go?’

I had no idea.