‘Last time I was out on an op in charge of four subordinates it was under heavy gunfire in Afghanistan and we had to make it across twenty miles of desert.’ He shrugged. ‘I think I’ll be OK. If Ms Yvonne continues with this speed I’ll see you there in ten.’

I bent down to Gigi. ‘Mummy’s going on ahead. You stay with Florence and her daddy.’

‘Bye, Mama. Bye bye.’ Gigi kept swinging Florence’s hand as they walked.

I swiftly overtook the rest of the nursery group and Yvonne and her flag.

There was nothing like being relieved of your two-year-old to realise how free you feel being able to walk at a good speed. I headed straight to the Marine Invertebrates room. Another group of school children were already in position on the floor waiting for Prehistoric Pete’s arrival. I looked around. The display cabinet at the back of the room was the one closest to the library door opposite. We already had its exact dimensions from Duggers and Frederick’s previous reconnaissance visit. As long as the measurements were correct the Etch A Sketch should fit snugly into the gap between the floor and the curve of the cabinet.

I put my tote bag on the floor and rummaged inside. I pulled the Etch A Sketch out and, using my handbag to mask what I was doing, slid it under the display cabinet. If it was discovered, a lost toy from a careless child wouldn’t raise any red flags with security. They wouldn’t bother dissecting it to find the receiver carefully hidden inside.

I patrolled round the room, stopping for a token admiring glance at the exhibits in each display case. At the back of the room was another door that led out into a large corridor. The library was opposite it. There was already a ‘No Entry’ sign on the door and a rope cordoning it off. Slumped in a chair on the right of the library door was a uniformed security guard. He may have just been blankly staring at his phone but his presence was a sign they really weren’t taking any chances with the security for tomorrow’s event.

Yvonne and her flag finally entered. I watched as kids and parents filed in after her. Where was Frederick? More importantly where was Gigi? I kept scanning the faces of every child in the room.

It looked as though everyone was here except Frederick and his four charges. I checked my watch. I’d left them over fifteen minutes ago to walk thirty feet. Could someone have intercepted them? My heart rate sped up. Where the hell were they? I headed out the door and was making my way back down the corridor when I saw them.