Caleb came crashing back through the undergrowth. ‘What do you mean? Don’t be ridiculous!’ was all that he could say. In that moment I hated him with all my heart. He was the screech of tyres on tarmac; he was pointed shoes and a trimmed beard; he was a reflection rushing across windscreens; he was stupid classical music swelling above the fumes; he was schoolbags slipping from my mother’s shoulder as she ran; he was a low brick garden wall and a pool of blood. He was my fault, and a thing that could never be undone.

I’d jumped up to confront him, but when I saw the wild panic in his face something immediately shifted inside me. Across the clearing he’d been scratching his head in apparent confusion; now both hands were clawing at his crew cut, his cheeks, his throat. He jittered left and right in panicky circles, catching his feet, stumbling and swaying, and saying things like, ‘ridiculous, impossible, no,’ over and over again. A hole had opened up in me as Innocent bled out in my arms; the sight of Caleb’s distress now filled it. I realised he was as close to the person I’d been at the roadside as anyone I’d ever seen, and though it’s hard to explain why, my hatred for him morphed into a kind of guilt. Instead of punching him in the face, I tried to put an arm around him, but he flinched and lurched backwards.

I staggered after him, but my legs weren’t working properly and I hadn’t made it more than ten clumsy paces before I caught my foot on a vine and pitched headlong into a the tangled vegetation. Caleb stopped and turned to see what had happened. As I pushed myself upright my left hand closed over something that felt wrong. Luckily I didn’t grip it hard; if I had I might have cut myself. It was a machete. Caleb’s, definitely: the handle had the same military-rubberised effect, and the blade, where it wasn’t covered with mud, was that unmistakable newish blue. He must have dropped it as the gorilla charged. It was only as I held the knife up to Caleb that I saw the smear along its sharp edge wasn’t dirt, but blood.

We both noticed it and we both understood what it meant. Caleb had provoked the silverback to charge by disobeying Innocent. In doing so he’d created a danger from which our guide had tried to save him. Innocent had sacrificed himself. But the fatal injury he’d sustained hadn’t come from the silverback’s bared teeth. They would have caused a ragged slash. The deep clean cut to Innocent’s neck had come from the honed blade Caleb had been brandishing.