Out of the Dark — Norah Lofts

To Mr. Cornwall, it seemed as though he'd been through the first part before. The battle to live as a gentleman…the tiresome wife…the unsympathetic children. To be sure, he sometimes thought he'd detected flashes of wit and charm in Charlotte, his daughter by his first wife, and it was true that the son of his second marriage was both handsome and precocious. But could these two make up for all the disappointments with which life had so unfairly burdened him? And now, once again, his affair with the nurse was an added complication. The last time such a thing happened, his wife had most conveniently died, or at least she'd died most conveniently for her successor. But he hadn't asked questions, had he? And why should the present Mrs. Cornwall complain, when he'd dutifully legalized their relationship and given her both the protection of his name and the security of his social position?
As for this new nurse, at least history didn't seem to be repeating itself in that respect. She gave herself passionately and never asked for more. So it really wasn't his fault that it turned out the way it did, was it? He hadn't intended any real harm. He certainly didn't mean to hurt the two children he liked better than any of them. And above all, he'd never once reckoned on MURDER!