‘I sat among the plants while I drew a sketch of the fort,’ John said, with simple dignity. ‘A man can do two things at once.’

Buckingham grinned at him. ‘A man such as you can do a dozen,’ he said sweetly. ‘Show me your plan, John.’

John unfolded the paper and spread it on the little table before his master. ‘The fort is built like a star,’ he said. ‘And only half-finished on one side. Our trouble will be that the north side, on the strand, is facing La Rochelle over the sea and can be easily relieved by the French troops who are camped around the besieged city on the mainland. We hold the island, right enough, they will get no help from here. And the town of La Rochelle is holding out against the Papist French army. But there are sally ports all along the base of the St Martin’s fort wall and they have boats moored ready. We will have to cut them off from the mainland before they can be reduced.’

Buckingham looked at John’s sketch. ‘What about a direct attack? Never mind starving them. An attack against the walls?’

John’s mouth turned down. ‘I don’t advise it,’ he said briefly. ‘The walls are new-built and high. The windows look very deep. You can’t hammer your way in, and you will lose half your men trying to scale it.’

‘They have to be starved out?’

John nodded.

‘So if we put our army all around them on the landward side, can you build me a barrier to span the seaward side to prevent them getting ships in and out?’

John thought for a moment. ‘I can try, my lord,’ he said. ‘But these are high seas. It’s not like building a raft across the Isis, it’s like building a raft across Portsmouth harbour. The waves come very high, and if there is a storm, anything we built would be smashed.’

‘Surely if we have enough wood, and chains …’

‘If the summer weather remains calm it might hold,’ John said doubtfully. ‘But one night of high winds would smash it.’

Buckingham got up swiftly and strode forward, looking down on the fort. ‘I tell you, John, I cannot stay here seated before a little fort, looking at it forever,’ he said, his voice so low that no-one but Tradescant could hear him. ‘I am laying siege to them, and they are trapped inside the fort, right enough; but all I have to feed my men is what I brought in my ships. I need support as much as the fort. Their army and their suppliers are over a small channel of water, while my army and suppliers are many miles away. And their king is commanded by Richelieu, while my king …’ He broke off, and then saw John’s uneasy face.