Study this example situation:

Sarah went to a party last week. Paul went to the party too, but they didn't see each other. Paul left t he party at 10.30 and Sarah arrived at 11 o'clock. So:

When Sarah arrived at t he party, Paul wasn't there.

He had gone home.

Had gone is the past perfect (simple):

The past perfect simple is had + past participle (gone/seen/finished etc).

• Sarah arrived at the party.

• When Sarah arrived at the party, Paul had already gone home.

• When we got home last night, we found that somebody had broken into the flat.
• Karen didn't want to go to the cinema with us because she'd already seen the movie.
• At first I thought I'd done the right thing, but I soon realised that I'd made a big mistake.
• The man sitting next to me on the plane was very nervous. He hadn't flown before. or ... He had never flown before.

Compare the present perfect (have seen etc.) and the past perfect (had seen etc.):

- Who is that woman? I've seen her before, but I can't remember where.	- I wasn't sure who she was. I'd seen her before, but I couldn't remember where.
- We aren't hungry. We've just had lunch.	- We weren't hungry. We'd just had lunch.
- The house is dirty. They haven't cleaned it for weeks.	- The house was dirty. They hadn't cleaned it for weeks.

Compare the past simple (left, was etc.) and the past perfect (had left, had been etc.):