Four siblings come from Alexandria for their summer holidays at their uncle and aunt's mansion on the hill of Kastella in Piraeus. The eldest, Alexandra, is serious and more measured; Pouloudia - the literary persona of Penelope Delta - is more rebellious but also more concerned about the behaviors of children and adults; the youngest, Alexandros, who still wavers between the tenderness of his age and his effort to appear older. And finally, Antonis, who is called Trelantonis, because he is "mischievous and very naughty, and constantly found himself in trouble".

In Trelantonis, first published in 1932, the carefree nature of childhood, the pranks and mischiefs of Antonis, as well as those of the other three, and the adult world as perceived by young children, create the most clearly "children's" book by the great lady of Greek children's literature, Penelope Delta.