But after a whole five hours' work one Sunday afternoon, he finally got down from the stepladder, folded it up, and rested it against the wall. Then stood back to admire the finished masterpiece.
He beamed a smile of satisfaction at his first creation. He had to admit he was quite impressed by his own work. The intricate detail of the scaly hide. The dull but monstrous look in the eyes of the triceratops as it munched dreamily on a bunch of leaves by the lakeside. The fierce, hungry expression in the eyes of the tyrannosaurus. And the traces of blood around its fangs. He could almost smell it, and fancied he could see it start to trickle slowly over the lower part of its beak-like jaw.
It was this trace of movement, and the sparkle in the cold-blooded eyes of the creatures, that confirmed his belief in oils.
Mum was right, he thought, they really do bring a picture to life.
Feeling very pleased with himself, he went to fetch his parents and show them the fruits of his hard labour. What he did not notice as he left the winter garden was the trickle of blood on the fangs of the tyrannosaurus dripping down the canvas onto the tiled floor.
But it was a different kind of unease he felt when he ran into the garden that afternoon. And it went much deeper. Deep into the pit of his stomach, because the instant he came out through the back door, he could tell the place was empty. Not a sign of life anywhere.
The air too had gone quite still. No breeze through the bushes. No birdsong. Not even any sign of Stripes. He sensed a chill run up his back, and shivered.
Maybe they're out the front, he thought, hopefully. And ran round the side of the house to the front garden. Nothing. Only a garden fork driven into the lawn beside the flowerbeds. Presumably by his father. All at once, for some reason that he couldn't put his finger on, he felt terribly alone.
'Mum!' he called. 'Dad!'
He hurried back into the house. Maybe they're upstairs, he thought. And he dashed upstairs, still calling them as he went. But still he got no answer. He tore from room to room. The bedrooms. The bathroom. His father's study. Not a sign of them anywhere.
What Henry didn't know was that, while he was out in the back garden looking for them, they were in the front. And when he was running round to the front garden, they were just going indoors. And at the very moment when he spotted the garden fork in the lawn, they were passing the door to his studio in the winter garden. Parents being parents, they let their curiosity get the better of them. And went in.