Freed from external danger, writes Justin, Ptolemy devised a crime against their relatives. So, he began to intrigue against the widow of Lysimachus - his half-sister Arsinoe. First of all, he wanted to kill her two sons, which eventually could become dangerous rivals to him, and besides, Keraunus really wanted to take away from the former queen belonged to her rich city of Cassandra. To make it easier to achieve the desired, Ptolemy, as usual, I decided to act cunning: he pretended to be in love, and begged her sister to marry him. Another way, besides playing from other sisters herself, he could not get close to her children, the kingdom which has to be cleared. But Arsinoe knew that her brother will always be directed towards evil, so long did not give in to his advances. Seeing her incredulity, Ptolemy loudly declared, if he wants, together with her sons to run the state, and if he had not fought them because that would take away their possessions, but only because he wished to return to Macedonia descendants Lysimachus as a gift out of his hands. Suppose, he said, would send a sister to him the oath a witness, that he is ready to give; in the presence of this man, he swears in the face of domestic gods and bind themselves with what only wants vows. Arsinoe hesitated, not knowing how to do it. Finally, fearing more for the children than for themselves, and considering that their marriage it would provide at least the safety of his sons, Arsinoe Ptolemy sent to one of his friends - Dion. Ptolemy brought him in sanctuary of Zeus, the ancient Macedonian sanctuary, and he laid his hands on the altar touching the great images and sacred seat of the gods, vowed unprecedented and the most terrible oaths that quite sincerely asks sister's hands, that the roll-call her queen, and that he would not have other children besides her sons. After that Arsinoe was filled with the hopes and fears of dropping, she spoke with her brother. The expression on his face and his eyes, full of affection, promising loyalty oaths at least led to the fact that she agreed to the marriage with his brother, despite the protests of his eldest son, Ptolemy, to convince the mother that her cheating.