Check this paragraph:
I had been working in the garden for an hour when I heard the phone ring. It was Jamie. He was driving down to London on business. I had gone out in the garden when he left, so he had only been gone an hour. I knew he had some problem.
My question : why "left"? To me all verbs in the last sentence "had gone out", "left" and " had been gone" happen before I heard the phone. So all should be in past perfect because I heard the phone is the reference time.
I know sometimes with since, you don't use past perfect:
I saw Peter yesterday, I hadn't seen him for a while since he left for Germany."
The word 'since' in that case indicates the beginning of the action. But when is not since and in that paragraph, first the person went out in the garden then Jamie left. Or may be I should understand the sentence like this:
He had only been gone for an hour since he left and at the time of the leaving I was already in the garden.