Absyrtus, or Apsyrtus was, in Greek mythology, the son of Aeëtes and a brother of Medea and Chalciope. Medea was complicit in her brother's death. The Argonauts, because of their involvement in his death, were for a long time, held back from a return to their native land by Zeus.
Apsyrtus is described as having the look of a Phoenician merchant, black of beard and with rings in his ears, with a hooked nose and a gleam of copper in his face. Apsyrtus lived with his father Aeëtes. Across the courtyard of the palace lived his sisters Chalciope and Medea.
Jason and the Argonauts rescued Chalciope's shipwrecked sons and, with them, travelled on to the city of Aea to ask Aeëtes for the Golden Fleece in exchange for a heroic service. Aeëtes suspected his grandsons Phrontis and Melas had brought the warriors to threaten his throne.
In return for the Fleece he challenged Jason to harness two fire-breathing bulls to an adamant plow, to furrow and sow rows of dragon teeth (which Aeëtes supplied). The teeth would sprout armed men. Jason was required to kill the sprouted earth men.
Chalciope, worried for the safety of her sons, asked Medea to help the Argonauts in their quest. She hoped her sons could escape Aeëtes with the Argonauts. Medea agreed as she also wanted to save Jason. She made a charmed potion for Jason. She also advised him to throw a great stone among the earth men so that they would fight each other, and to hasten away from her father after they had secured the Fleece. With Medea's advice Jason succeeded in plowing the field and in killing the men.
Aeëtes, with Apsyrtus beside him, told his people to kill the Argonauts and burn their ship. Medea helped Jason gain the Fleece and escaped with him.
The escape of the Argonauts was cut off by Apsyrtus. Apsyrtus had men enough to overwhelm them, but he shrank from a fight with the heroes, and he thought that he might gain all he wanted from them without a struggle. Theseus and Peleus went to him. Apsyrtus wanted them to give up the Golden Fleece, Medea and the sons of Chalciope. Theseus and Peleus argued that the Fleece had been fairly won by completing the task. Apsyrtus agreed, but Medea would have to be given to her brother. If that were done the Argo would be let go on her course, Apsyrtus said, and the Golden Fleece would be left with them. Apsyrtus said, too, that he would not take Medea back to the wrath of her father; if the Argonauts gave her up she would be let stay on the island of Artemis and under the guardianship of the goddess.
Medea did not agree to go. She and Jason made a plot to deceive Apsyrtus. They decided to take Medea off the island of Artemis secretly. Medea then was left by the Argonauts on the island of Artemis. Apsyrtus had been commanded by his father to bring Medea back to Aea; he thought that when she had been left by the Argonauts he could force her to come with him. So he went over to the island. Jason, secretly leaving his companions, went to the island from the other side.
By the temple of Artemis Jason and Apsyrtus came face to face. Both men drew their swords. Then, before the vestibule of the temple and under the eyes of Medea, Jason and Apsyrtus fought. Jason's sword pierced the son of Aeetes as he fell Apsyrtus cried out bitter words against Medea, saying that it was on her account that he had come on his death. And as he fell the blood of her brother splashed Medea's silver veil.
Jason lifted Medea up and carried her to the Argo. They hid her under the Fleece and sailed past the ships of the Colchians. When darkness came they were far from the island of Artemis. It was then that they heard a loud wailing, and they knew that the Colchians had discovered that their prince had been slain.
They had escaped the danger that had hemmed them in, but the Argonauts, as as they went on through the darkness heard the voice of the ship. The voice proclaimed the wrath of Zeus on account of the slaying of Apsyrtus. The Argonauts would have to wander forever over the gulfs of the sea unless Medea had herself cleansed of her brother's blood. There was one who could cleanse Medea--Circe, the daughter of Helios and Perse, and sister of Aeëtes. The voice urged the heroes to pray to the immortal gods that the way to the island of Circe be shown to them.
Source:
http://en.wikipedia.org/wiki/Absyrtus
http://ancienthistory.about.com/library/bl/bl_text_colum_part2_d.htm