Free The Impossible Clue by Sarah Rubin

Mercedes. There were two men sitting in the front. They looked perfectly normal, and I felt foolish for being suspicious.
    â€˜Here,’ I leant in through the window and handed Dad his and Della’s share of the food. He needed to go to the office to pitch his story and it was quicker for me to walk home from the museum rather than the Walnut StreetTheatre.
    â€˜I’ll see you back at the house,’ Dad said, and swerved back into the traffic.
    I watched Dad drive down Race Street. The silver Mercedes was right behind him. For some reason they didn’t look like tourists any more. I felt a cold knot twist in the pit of my stomach. I grabbed my phone and snapped a picture right before the car turned on to 21st Street. The same direction my dad had gone. I was getting ready to dial 911 when I noticed the next three cars turning in the same direction. There were roadworks at the end of the street. All the cars were turning that way. This Delgado case was making me jumpy.
    I shook myself and started the walk home, counting my steps as I went. The city smelt of summer – hot concrete and the things that stuck to it. I took a swig of my cherry cola and tried to shake off my gloom. I knew what the problem was. The case was too important. I’d lost track of how many mysteries I’d solved for people at school. But finding the basketball team’s missing bake sale money was one thing. Finding a missing scientist working on a top secret invisibility project . . . that was a whole new level.
    I took a breath and thought about maths. Even the most complicated equations can be simplified. I just needed to look at all the factors and break them down. According to the security camera, Dr Learner hadn’t left his office. That meant there were four possibilities. One: there wasanother exit from Dr Learner’s office. Two: someone had tampered with the security camera. Three: Dr Learner was still in his office now. Four: Dr Learner was invisible.
    I laughed to myself. As impressive as Graham Davidson’s demonstration had been, I just couldn’t believe Dr Learner had made a working invisibility suit. A breakthrough in the right direction, maybe, but not a working suit. I like to see things before I believe them. Although I had to wonder, could you see an invisibility suit or was it invisible? I laughed a little louder and a man screaming into his mobile stared at me like I was crazy. I ignored him and kept walking.
    It took about twenty minutes to get home. The pale strip of skin where I parted my hair burnt and I knew brushing it later would be like holding a match to my scalp. My shirt clung to the small of my back. It might as well have been raining. I gave a sigh of relief when I saw our front steps. And then I sighed again. Sammy Delgado Jr was sitting on them.
    â€˜Alice!’ he shouted, jumping up. He was wearing pressed tan shorts, a blue button-up shirt and a navy-blue blazer. He looked like something out of a sailing magazine. ‘Hi. I was waiting for you. We didn’t get to talk yesterday.’ Sammy blushed and looked at his shoes. He was probably remembering that the last time I saw him he was running out of a room in tears.
    â€˜Hi Sammy.’ I stepped past him and unlocked the frontdoor. Sammy stood on the top step watching me, the way a dog watches you when you’re making a sandwich.
    â€˜Would you like to come in?’ I asked. I didn’t have much of a choice.
    It was like I’d offered him a ticket to Disney World. He bounded in and then stood there, unsure of what to do next.
    â€˜Sit down,’ I said, nodding toward the couch on the living-room side of things. ‘I’ll get us a drink. What do you want?’ I opened the fridge and stood staring at the practically-empty shelves, trying to soak up the coolness. ‘We have water.’
    I needed to remind Dad to go shopping.
    â€˜Water’s good,’ Sammy answered.
    â€˜So why are