Toxin (en Inglés) - Ouida

When a precious opal heirloom slips from a young widow's throat into the Venetian lagoon, no one imagines what the loss will set in motion. Months later, the necklace washes up on a forgotten marsh island -- and into the hands of two travelers whose meeting will alter every life it touches.

One is a generous Sicilian aristocrat, warm-hearted and barely twenty-four. The other is a brilliant English surgeon who has long since traded conscience for the cold pursuit of physiological knowledge, a man who regards human beings as little more than specimens for his blade.

Returning the necklace to its owner draws all three into a fatal triangle. The young nobleman courts the widow with sincere devotion; the surgeon, unable to win her by warmth, sets out to possess her by other means. As one will steadily bends another, a quiet poisoning of body and spirit unfolds beneath the songs of the gondolier.