Construction: had + participle (worked, saved)
(1) Past perfect is used to talk about a completed action before the past (the past before the past).
- I had left the office before 18h yesterday.
- You had not told me about this before.
- She explained to me that she had completed the project.
(What is highlighted in red are verbs or adverbs that denote the past, thus the past perfect must follow because the action is a completed action in a past before the past).