We can use the past perfect with the past simple when we talk about two actions or events in the past.
- I phoned the office, but Emma had already left.
We use the past perfect for the action that happened first. We often use already/just with the past perfect to say when it happened.
- I ran to the station, but the train had already left (some time earlier).
- I arrived at the bank, but it had just closed (a very short time earlier).
We use the past simple for the most recent action.
- When I got there, the train had already left.
- After he'd done the washing, he cleaned the windows.
We can use the past simple when one action comes immediately after another.
- He did the washing and then he cleaned the windows.
We use the past perfect with the past simple to give a reason for a situation. We use the past simple for the situation, and we use because + past perfect for the reason.
- I was happy (the situation) because I'd got tickets for the festival (the reason).