Since Diktys and Polydektes were sons of Androthoe daughter of Perikastor and Peristhenes son of Damastor son of Nauplios son of Poseidon and Amymone, as Pherekydes says in the first book (translation by Silvio Curtis).
When Perseus was living in Seriphos with his mother and had grown into a young man, Polydektes, Diktys’s brother through his mother, king of Seriphos, happened to see Danae and desired her, but he was at a loss how to sleep with her. And he prepared a lunch and invited both many others and Perseus himself. And when Perseus asked what price the meal was being celebrated for, and he said for a horse, Perseus said for the head of the Gorgon. But after the meal on the next day, when the other participants brought in the horse, Perseus did too. And Polydektes wouldn’t accept it, but demanded the head of the Gorgon according to the promise. And he said that if he didn’t bring it to him, he would take his mother. And Perseus went away sorrowfully, mourning the disaster, to the end of the island. But Hermes, seen by him and bringing the question to him, learns the reason for the lament. And he leads him first, telling him to cheer up, to the Graiai, daughters of Phorkos, Pemphredo and Enyo and Deino, with Athena preceding them, and he steals away their eye and their tooth as they hand them to each other. And they, noticing, cry out and supplicate him to give back the eye and the tooth, because the three of them made use of one by taking turns. And Perseus says he has it and he will give it back if they direct him to the nymphs who have the cap of Aides and the winged sandals and the pouch. And they tell him, and Perseus gives back what he took. And he goes away to the nymphs with Hermes, and after asking and getting them he ties on the winged sandals and hangs the pouch on his shoulders and sets the cap of Aides over his head. Then, flying, he goes to the ocean and the Gorgons, with Hermes and Athena following with him. And he finds them sleeping. And the gods with him explain to him how he must cut off the head while turned away, and they show him Medousa, who alone was mortal of the Gorgons. And he gets near and cuts it off, and puts it into the pouch and flees. But they notice and chase him and don’t see him. And Perseus gets to Seriphos, goes to Polydektes, and tells him to collect his people so he can show them the Gorgon’s head, knowing that if they saw it they were going to be rocks. And Polydektes assembles the crowd and tells him to show it. And, turning himself away, he takes it out of the pouch and shows it. And when they saw it they turned to rocks. But Athena takes the head from Perseus and sets it in her aegis. And he gives the pouch away to Hermes, and the sandals and the cap; and Hermes gives them back to the nymphs. And Pherekydes records it in the second book (translation by Silvio Curtis).
So he [Polydectes] called together his friends, including Perseus, under the pretext of collecting contributions towards a wedding gift for Hippodamia, daughter of Oenomaus (original Greek).