The difference between the past simple and the past perfect

When the events of a story are told in the order in which they occurred, the past simple tense is used:

I missed the last bus, so I only got home at about 6 o'clock. I was really tired, so I took a hot bath. Then I made some dinner and watched a film. At 10, I was in bed.

However, if the events are told in a different order or there are references to an earlier time, the past perfect tense is used to express the earlier events:

I only got home at about 6 o'clock because I had missed the last bus. I was really tired, so I took a hot bath. Then I made some dinner and watched a film I had borrowed from my friend Sheila earlier that week. At 10, I was in bed. It had been a long day.