The Greek writer Plutarch, in his essay On Isis and Osiris composed around the end of the first century CE, preserves a myth episode absent from the older Egyptian funerary texts but influential ever since it was written down: that Osiris, deceived in darkness, slept with Nephthys believing her to be her sister Isis, and that Nephthys, fearing the anger of her husband Set, concealed the child born of that encounter as soon as he arrived. Isis, learning of the birth, searched him out with the help of dogs that led her to him, an origin story Plutarch offers for why dogs were kept as sacred, watchful animals in Egyptian religious practice, and she raised the abandoned infant, the jackal headed Anubis, as her own protector and attendant rather than casting him aside for the circumstances of his birth.
Plutarch was writing several centuries after most of the native Egyptian sources that mention Nephthys, working partly from Egyptian priests and partly from earlier Greek accounts now lost, and Egyptologists read On Isis and Osiris as a valuable but syncretic witness, useful for the sequence and emotional shading of episodes it preserves while requiring care about where a Greek philosophical frame has reshaped older Egyptian material. Whatever its precise fidelity to earlier belief, the story gave later readers, ancient and modern alike, a rare moment of ordinary human frailty inside a family of gods otherwise defined by cosmic mourning and vengeance, and it is largely through Plutarch's telling that the Nephthys and Anubis connection reached the wider ancient Mediterranean world at all.