Shadow's End by Thea Harrison — book slip

For Beluviel, consort to the Elven High Lord, and Graydon, gryphon and First Sentinel of the Wyr, even the slightest desire for each other is forbidden. But two hundred years ago, after a desperate play to save Beluviel’s stepson left them indebted to the cruel Djinn Malphas, they found their fates inexorably linked together—and the hunger between them growing too strong to ignore…

Two centuries later, with their debt to Malphas coming due, Beluviel and Graydon realize that, if they are to stand any chance of saving their souls, they must once again work together—this time more closely than ever before. But every moment they spend with each other brings them nearer to losing something even more vital—their hearts…