By the time the aquarium opened on Saturday, Tank Seven was empty and a trail of wet circles crossed the floor. Niko, whose mother cared for the marine animals, knew at once what had happened. Ink, the young common octopus, had escaped again.

Most visitors imagined octopuses as soft creatures drifting wherever the current pushed them. Ink was more like a puzzle expert with eight arms. She could unscrew jar lids, squeeze through gaps narrower than Niko's wrist and remember which coloured door hid her food. Last week, she had learned to lift the corner of her tank cover. This week, someone had forgotten the extra latch.

Niko followed the damp marks past the jellyfish gallery, but they vanished beside a row of dark storage tubs. He stopped searching with his eyes and started thinking like Ink. An octopus without bones would choose the smallest, darkest shelter nearby. He checked a bucket, a drain and an empty pipe. Then he heard a faint splash from a plastic watering can.

Ink had folded her whole body through its narrow spout and settled inside the cool water. Niko placed the can beside Tank Seven and tipped it gently. One arm appeared, then three, then all of Ink, changing from sandy brown to bright red as she explored her home. This time, Niko fastened both latches himself.