Aratus (20.2-20.3)

Having come, therefore, to the place appointed, he was waiting for Erginus to come there with Diodes, just outside the city, near what was called the Ornis. As he was waiting, however, the oldest brother of Erginus and Diodes, named Dionysius, who was not privy to the enterprise and took no part in it, but resembled Diodes, chanced to come up. So Technon, moved by the similarity in the marks of his outward appearance, asked him if he was connected at all with Erginus;

and on his saying that he was a brother, Technon was altogether convinced that he was talking with Diodes, and without inquiring his name, or waiting for any other proof whatever, gave him his hand and began chatting with him and asking him questions about what had been agreed upon with Erginus. Dionysius took cunning advantage of his mistake, assented to all that he said, and turning his back towards the city led him along in unsuspicious conversation.