The Seven Streams by Warwick Deeping

Tristan, made his way back to the boat, poled out from the island, keeping its black shadows betwixt him and the nearest galley. He rowed eastwards into the open cavern of the night, his eyes roving from the distant town to the great ships stealing over the water. Their tall masts rose against the last gleaming cranny in the west. Beyond them the mountains towered solemn and stupendous, fringed with aureoles of transient fire. Even in the half gloom Tristan could see a vague glittering movement on the slopes behind the castle, a glitter that told of armed men marching from the hills. It grew plain to Tristan, as his broad back swung with the oars, that the Pope's men had come by sea from the Southern Marches, sailed up the great river, landed troops in the woods, struck a sudden blow at the chief lord of the province of the Seven Streams. While Ronan had grown drunk with the strong wine of jealousy, Death had descended upon Joyous Vale, and sprinkled the Cross with the blood of sacrifice.

There was a swirl of thought in Tristan's brain. Rosamunde of Joyous Vale had his mind in thrall, and his first duty to her was easy in its consummation. Leaning his chest upon his oars, he reached for the casket where it lay on the plankings at his feet. The thing was bound with iron, its wood black and ponderous with age. Tristan balanced it in the hollow of his hand, wondering whether it would sink or swim. The feminine temptation to force the lid never thrust a suggestion into his brain. Tossing the casket over the gunwale, he saw it sink in a wavering circle of light. For fully a minute he watched the place, that he might be assured of the casket's burial. With the vow to Rosamunde fulfilled, he turned both his thoughts and his boat towards the shore.