“Yeah, well, that’s partly why I’m showing you. Just to say keep your eyes out for it opening. You can help me pin it inside a case.” The two men grinned.

From below came a series of bangs, like water fighting its way through obstreperous plumbing. There was a faint hiss of pistons. Isaac and David stared at each other, nonplussed for a moment.

“Sounds like the cleaner’s gearing up to some serious action,” said David.

In the short, stubby byways of copper and brass that were the construct’s brain, a welter of new data and instructions clattered violently. Transmitted by pistons and screws and innumerable valves, the grots and gobs of intelligence bottlenecked in the limited space.

Infinitesimal jolts of energy burst through tiny, finely engineered steamhammers. In the centre of the brain was a box crammed with rank upon rank of minuscule on-off switches that puttered up and down at great and increasing speed. Each switch was a steam-powered synapse, pushing buttons and pulling levers in intensely complicated combinations.

The construct jerked.

Deep in the construct’s intelligence engine circulated the peculiar solipsistic loop of data that constituted the virus, born where a minute flywheel had skittered momentarily. As the steam coursed through the brainpan with increasing speed and power, the virus’s useless set of queries went round and round in an autistic circuit, opening and shutting the same valves, switching the same switches in the same order.

But this time the virus was nurtured. Fed. The programmes that the repairman had loaded into the construct’s analytical engine sent extraordinary instructions coursing throughout the crafted tubework cerebellum. The valves flapped and the switches buzzed in staccato tremors, all seemingly too fast to be anything but random motion. And yet in those abrupt sequences of numerical code, the rude little virus was mutated and evolved.

Encoded information welled up within those limited hissing neurones, fed into the recursive idiocy of the virus and spun out from it skeins of new data. The virus flowered. The moronic motor of its basic, mute circuit sped up, flung blossoms of newborn viral code spiralling away from it with a kind of binary centrifugal force, into every part of the processor.

Each of these subsidiary viral circuits repeated the process until instructions and data and self-generated programmes were flooding every pathway of that limited calculating engine.

The construct stood in the corner, shaking and whirring very slightly.

In what had been an insignificant corner of its valved mind, the original virus, the original combination of rogue data and meaningless reference that had affected the construct’s ability to sweep floors, still revolved. It was the same, but transformed. No longer a destructive end, it had become a means, a generator, a motive power.