The sky over the ridge had turned the colour of a bruise by the time the bell went. Ren stood at the school gate with his bag over one shoulder and watched the first fat drops darken the footpath, one by one, like someone testing paint.

'We'll go the drain,' said Diego, appearing beside him. 'Twenty minutes instead of forty. Easy.'

The drain was a concrete stormwater channel that ran under the highway and came out behind the shops near Ren's street. In the dry it was a wide, echoing tunnel where kids rode their bikes and sprayed their names on the walls. He had seen it after rain, when the trickle in the middle became a brown, roaring thing that carried shopping trolleys and tree branches and once, famously, a letterbox.

'It's about to bucket down,' said Ren.

'It's about to bucket down, which is why we go now.' Diego was already walking. 'You coming or not?'

That was the thing about Diego. He never argued. He just moved, and let you decide whether to be the one left behind.

Ren followed him. He told himself it was because of the rain, but he knew it was really because Diego had said you coming or not in that particular voice, the one that made staying behind feel like a verdict.

They reached the mouth of the drain as the rain began properly. Water was already running down the sloped concrete in sheets and gathering in the channel, ankle-deep and fast. The tunnel ahead was a black oval with a grey coin of light at the far end.

'Diego.'

'It's fine. It's a puddle.'

'It's not a puddle. Look at it. It's moving.'

Diego looked at it, and for a second Ren saw something flicker across his face, something that might have been doubt. Then it was gone, and Diego grinned and stepped into the water. 'Four minutes. Time me.'

Ren stood at the edge. The rain hammered on his bag. He thought about the letterbox. He thought about Diego's face, that flicker. He thought about how it would feel to be the one who went home the long way, alone, and how it would feel to be the one who didn't.

'I'm not coming,' he said. It came out louder than he meant, and echoed down the tunnel after his friend.

Diego stopped, ten metres in, the water pulling at his shoes. He didn't turn around straight away. When he did, the grin was gone.

'Seriously?'

'Seriously. Come back. We'll go the long way and I'll shout you a pie.'

For a long moment Diego stood there in the dark with the water tugging at him, and Ren understood that he was not deciding whether the drain was safe. He had known that at the entrance. He was deciding whether he could turn around without it meaning something.

Then a branch came down the channel, thick as an arm, spinning, and knocked against Diego's shin, and the decision was made for him. He came out of the tunnel fast and not quite steady, and stood beside Ren in the rain, breathing hard.

They walked the long way. It took fifty minutes, not forty, because the footpath along the highway flooded and they had to climb the embankment. At the shops Ren bought two pies, and Diego ate his without a word, and when they reached Ren's street Diego said, 'Tomorrow, if it's dry,' and Ren said, 'Yeah, if it's dry,' and that was as close as either of them came to saying what they meant.