Milne nodded. In truth, though, he wasn’t sure if he would send for him. It was the very devil of a thing to judge.

‘No, Captain Hart, I must do it myself. I do appreciate that it is a sapper’s business, but in the pitch dark without having seen it, you’ll have the devil of a job.’

The captain of Madras Pioneers had done all that honour demanded. Even when he’d conceded that a boat of any sort was bound to be seen in the moonlight, Fairbrother was adamant that neither he nor any of his sappers enter the water with him. He would swim with just Abhina, the hijda with whom he’d ‘fished’ in the moat the day before (and who’d promised the sentries many good things to let them), and with Askew, whom he’d come to trust. Even if there’d been no moon, he’d have insisted on it. In truth, closing the sluice would be the easiest of things, especially for a sapper. It hardly needed exploration. But if the tunnel was to be the means by which the evil of Ashok Acharya – and all his fugitive thugs – was brought to an end, then he wanted it to be by his hand. For Abhina had told him of Mira Bai.

Nor indeed would the tunnel be retribution enough. He would seek out the strangler and do to him what he’d done to that brave, dutiful and noble-born woman, wife of that fine old gentleman-soldier and mother of his children – the man without whom they’d be hard-pressed now to know what was right to do, let alone how to do it.

‘And I cannot persuade you to have a boat ready to assist in case of mishap?’

Fairbrother shook his head. ‘The risk’s too great. There are no muggurs, I assure you.’

Captain Hart was a man of scientific training. He accepted that Fairbrother had seen none, and that at night the muggur’s habit was to come on land, but neither of these ‘facts’ was a basis for certainty. That the three were taking with them knives the size of hatchets seemed to argue his case for him. All he could do, however, was give him his hand and let them go into the night.

And then wait and trust he was right to do so.

A little while later at the champak bush, the marker for the crossing, the three of them stripped to just a loincloth, slid into the water and began silently to swim, Askew with a capped pistol wrapped in oilskin between his teeth.

The moat wasn’t wide by the standards of the great fortresses of Hindoostan, or even deep, its purpose more to prevent the walls being taken by surprise than to withstand prolonged siege. Even swimming cautiously, reaching the sluice didn’t take long, the moon giving them just enough light to see their line. Nor did closing it require any great effort, for gravity was on their side. There was just the faintest groan of the pulley as it lowered, nothing that the most bat-eared of sentries in the tower above could have heard. Yet Fairbrother wasn’t content until he’d made sure the sluice gate was firmly seated. Three times he dived, coming up between for air with as little sound as a fish might make rising to the fly. Throughout they spoke not a word – as if anything much had been possible with Abhina – managing with hand signals alone.