Could you help me identify this story?

Envae

Please could someone help me identify this story - I believe it was Agatha Christie, but I may be wrong.  Many years ago I read a short section of a story and have no idea what it was called.  I would love to be able to find it and read it in its entirity.  The section I remember - set in 40s/50s I think.  3 children (boys) who live in a large, wealthy house wake up early and decide to sneak out into the garden to play in the swimming pool.  They are playing with a ball in the water.  A man from the household walks past them with a newspaper, says something to the boys and goes through a doorway in a hedge/maze that is next to the pool.  One of the boys throws the ball and it goes over the hedge so he has to go and retrieve it.  As he enters the hedge/maze area he finds the man who had recently passed them on the floor with a head wound (unsure if he was dead or just unconcious).  The remaining boys in the pool call out to him asking why he is taking so long then silently the ball is thrown back over the hedge but no sign of the boy who entered to retrieve it. 

If anyone could tell me what this story is, I would be very grateful.  Thank you

GKCfan

I'm sure this isn't an Agatha Christie story.  I'm not sure who actually wrote it, though...

Tommy_A_Jones

I am almost Positive it isn't an Agatha Christie story.

shana

This is a familiar story, but I agree not one AC wrote. If I am not mistaken it has also been made in a motion picture. But I don't have specifics.

Envae

Thank you for taking the time to answer. It's driving me crazy trying to find out what this story is. I'll keep searching...