SOLVED. YA Mystery - Abandoned hall in Cornwall with hidden creatures brought back from the Amazon ~2005

[Jake]

I listened to this as an audiobooks on a cd in about 2005, the cd cover had a picture of a cast iron gate on it.

An orphan (steven?) Whose parents died in a car crash is working in a rare plant garden in London. A man comes by and tells him that his uncle has died and he has inherited an abandoned hall in Cornwall, at the same time a rare flower, which blooms only once comes out.

He travels to Cornwall, stopping to rest in some watercress, and finally arrives at the hall. It is abandoned but has a feel that there is something there.

He starts reading his uncles notes from an expedition to the Amazon where he got malaria and was hallucinating and lives with a tribe that has since been wiped out.

Eventually he finds a blue and yellow snakey creature that it turns out his uncle bought back from the amazon and needs him to look after to protect the secret.

Any ideas?

[Jake]

I think the title had "secret" in

[Jake]

Solved, it was The Valley of Secrets