Lynceus was born in the royal house of Egypt as one of the fifty sons of King Aegyptus. His mother was Argyphia, a woman of royal blood, and his full brothers were Proteus, Busiris, Enceladus, Lycus and Daiphron. His father traced his line to Belus, brother of Agenor, and ultimately to the wanderings of Io from Argos to the Nile. Aegyptus ruled in Egypt and possessed an army large enough to enforce his will. His twin brother Danaus had fifty daughters, the Danaids, and the two houses should have been joined by marriage. Instead, the rivalry between the brothers turned the proposed alliance into one of the darkest stories in Greek myth.

Danaus feared the intentions of Aegyptus and his sons. When the brothers' rivalry turned towards marriages between their children, he fled from Egypt with his fifty daughters. Apollodorus credits him with building the first ship under Athena's advice, a claim belonging to myth rather than maritime history. They reached Argos, but the accounts of their reception differ. In Aeschylus' Suppliants, King Pelasgus faces the difficult choice of sheltering the Danaids or risking conflict with their Egyptian pursuers. The daughters cling to the altars and appeal to Zeus, god of suppliants. In Apollodorus's account, the reigning king Gelanor surrenders the kingdom to Danaus. These are different treatments of the family's arrival, not a single sequence in which Pelasgus accepts them and then Gelanor is overthrown.

The quarrel followed the fugitives to Argos. Hyginus tells how Aegyptus sent his sons after Danaus with orders to kill their uncle or never return. They attacked him, and Danaus, unable to resist them, agreed to the marriages to end the fighting. Apollodorus gives a different emphasis: the sons asked Danaus to abandon his hostility and let them marry his daughters, and he consented despite his distrust. Fifty bridegrooms and fifty brides would be joined on the same night in one enormous wedding. The spectacle concealed a massacre. Danaus gave his daughters daggers and ordered them to kill their husbands as they slept. Pausanias connects the severed heads with the daughters' proof to their father that they had carried out the deed.

Lynceus was paired with Hypermnestra, the eldest daughter of Danaus by Elephantis. Ancient accounts offer different reasons for what followed. Apollodorus says Lynceus respected her virginity and that she spared him for that reason. Ovid places the story in the voice of Hypermnestra herself, torn between her father's command and her horror at killing her sleeping husband. His poem gives her repeated hesitation, an inability to carry out the murder and the decision to wake Lynceus and urge him to flee. Love, compassion and loyalty to the marriage bond have all shaped readings of her act. Whatever the emphasis, she refused to do what her father demanded while her sisters moved against their husbands.

The wedding night became a slaughter. Forty-nine sons of Aegyptus were killed in their beds by the brides they had just married. Only Lynceus survived. Hypermnestra helped him escape from the chamber and guided him out of Argos before Danaus could discover what had happened. The palace filled with blood, severed heads and the cries of the dying while Lynceus fled through the darkness. His life now depended upon a woman who had broken her father's command.

Hypermnestra sent him towards Lynceia, a city in the Argolid. To reassure one another across the distance, they used fire. Lynceus raised a torch from Lynceia to show that he had reached safety. Hypermnestra answered with a torch from the citadel of Larisa at Argos. The Argives later preserved the signal in a torch festival, turning the lovers' flight into a civic ritual. Lynceia itself carried Lynceus' name and made his escape a permanent part of Argive geography.

Danaus discovered Hypermnestra's disobedience and treated it as a betrayal. Apollodorus says he imprisoned her. Pausanias reports that her father brought her to trial and that the Argives acquitted her; afterwards she dedicated an image of Aphrodite to commemorate her escape. The trial placed filial obedience against mercy and the marriage bond. A surviving speech from Aeschylus' lost Danaids gives Aphrodite a celebration of desire joining sky and earth, with rain making the earth fruitful. That speech is often connected with a defence of Hypermnestra, but the complete play has not survived and its courtroom setting cannot be treated as certain. The fragment makes love a force in the natural order; Pausanias separately preserves the tradition of the daughter's acquittal.

What Lynceus did next varies by teller. Retellings of the cycle include an avenging Lynceus who kills Danaus, but that ending should not be assigned to every ancient source. Apollodorus says that Danaus later united Hypermnestra with Lynceus and that Lynceus subsequently reigned over Argos; he does not narrate an invasion from Egypt or explain Danaus's death. Hyginus gives another detail: Abas brings Lynceus news of Danaus's death, after which Lynceus rewards him with a shield. Ovid's Heroides 14 ends with Hypermnestra appealing for rescue, not watching Lynceus kill her father. The surviving accounts therefore support his eventual kingship without providing one universally agreed passage from massacre to succession.

The consequences of Lynceus' survival were enormous. He and Hypermnestra had a son, Abas, who inherited the Argive throne. Abas fathered the rival twins Acrisius and Proetus, whose quarrel divided Argos. Acrisius had a daughter, Danae, whom Zeus visited in the form of a shower of gold. Their child was Perseus, slayer of Medusa and founder of Mycenae. Through Perseus's line came Alcmene and Heracles. In this genealogy, the Perseid line and the descendants of Heracles therefore trace their ancestry to the wedding night when Lynceus alone escaped death. The son of Aegyptus became a founding ancestor of an important Greek heroic dynasty.

His brothers did not receive the same continuing royal genealogies. Pausanias places their severed heads near the approach to Larisa at Argos and their bodies at Lerna. Apollodorus instead places the heads at Lerna and the funeral honours for the bodies before the city: the burial locations vary between accounts. In Apollodorus, Athena and Hermes purify the Danaids at Zeus's command, not the ground. Hyginus associates the other sisters with an Underworld punishment of carrying water in perforated vessels, while Hypermnestra is distinguished by her refusal to kill. The division between the sisters made Lynceus' survival a moral divide: one night, fifty marriages, and one wife's mercy carrying the dynasty forward.

The torch ritual preserved his story in Argive public life. The commemorative fire signal between Lynceia and Argos transformed a private reassurance between husband and wife into a performance of civic memory. Argos did not hide the massacre that founded the dynasty. Its local traditions remembered the escape, the trial, the spared bridegroom and Hypermnestra's association with Aphrodite. Through Lynceus, the Egyptian royal house entered Argive kingship. Through Hypermnestra, the city gained a myth in which mercy overcame obedience.

Ancient writers gave the story immense dramatic force. Aeschylus' Suppliants presents the Danaids' flight to Argos and their demand for protection before the marriages occur. The lost Egyptians and Danaids belonged to the same dramatic cycle, but the details of their action must be reconstructed from fragments and related testimony. Ovid's Heroides fourteen transforms Hypermnestra into a first-person narrator writing to the absent Lynceus, defending her refusal and asking why innocence should suffer for obeying the greater command of love. Later mythographers simplified the tale into a compact sequence of pursuit, marriage, massacre, escape and succession.

The story of Lynceus and Hypermnestra became a favourite subject for moral and artistic interpretation. The spared bridegroom represented survival through female mercy. Hypermnestra's act placed marriage and compassion above the absolute power of a father. The surviving speech assigned to Aphrodite placed desire within the order of nature. The torch exchange became an image of trust across separation. The Danaid punishment turned Lynceus into the exception whose life exposed the guilt of all the others.

This Lynceus must not be confused with his Messenian namesake. The son of Aegyptus never sailed on the Argo, never hunted the Calydonian Boar and never fought Castor and Pollux. His world is the Danaid tragedy: Egypt, Argos, the fifty marriages and the one bride who disobeyed. His defining trait is survival, not supernatural vision. His identity is established by his parentage and marriage, not by the exceptional eyesight of the Argonaut. In the local tradition, Lynceia took its name from him and remembered the place from which he signalled that he was still alive.