He rang the lab inside the gargantuan facility, just in case one of them had arrived for work before him. None of them had. All four of them worked in the neurocellular research section, investigating the neurotransmitters responsible for reward pathways. Their lab was affectionately known as the Happy Bus, because part of their work involved creating newer and better antidepressant drugs. The irony, which wasn’t lost on their associates, was that it was indeed a happy lab. Alex realised with a painful pang of panic that he was growing more perturbed by the minute for his friends.

‘Have any of them checked in at all overnight?’ he asked the lab coordinator.

‘No, Alex. I haven’t seen them at all. I thought George was on holiday.’

‘He was due back yesterday. It’s just that I think I’m coming down with flu, and I wanted to let them know I won’t be in today.’

‘Ah, no worries, I’ll tell them as soon as they come in. Get well soon. Take care of yourself, there’s a lot going around…’

Alex started up the engine again and swung out of the car park, directly underneath a CCTV camera.

George lived in Wanstead, in a town house tucked away behind mature trees and a stone wall. Alex had been to dinner there many times. George lived alone, and had done since his divorce. The death of his daughter had driven a wedge between him and his wife that could never be removed. But that was a long time ago, and George had never remarried.

Alex parked along the street and walked to the house, going straight around the back. The gate was unlocked and he peered through a few windows, seeing nothing. There were no lights on, or any movement of any kind. The back garden was George’s pride and joy. Blooms exploded all over as the plants and trees sucked the goodness out of the June light, thriving in their well-chosen plots. A pond glimmered in the early-morning sun, and the sound of rushing water over the rocks and reeds made Alex smile. He imagined George sitting here reading The Lancet or some medical tome, with his cup of tea and a couple of ginger biscuits.

The shed was at the bottom of the garden, and he followed the path to it. It was locked. Birds chirped, and bees flitted between lavender and jasmine. Alex knew that the key was kept under a pot behind the pump for the pond’s water feature. He took it out and unlocked the shed door. It didn’t take long to locate the bunch of keys for the lab.