One hour's work, a day's wage — and the complaint the story wants to provoke.
A landowner goes out at dawn to hire workers for his vineyard and agrees with them on a denarius for the day. He goes back to the marketplace mid-morning, at noon, mid-afternoon and an hour before sunset, and hires more each time.
At the end of the day he has them paid starting with the last. Everyone gets a denarius. It is the parable that most annoys first-time readers, and it is built to.
Isn't it lawful for me to do what I want to with what I own? Or is your eye evil, because I am good?
An "evil eye", in the idiom of the time, was envy — looking at what someone else got and feeling robbed. The first workers were not cheated: they got exactly what they agreed to. What bothers them is not their own pay but the generosity to others. The landowner asks whether his goodness has become an offence.
Just before, Peter had said: "Behold, we have left everything, and followed you. What then will we have?" (Matthew 19:27). The story is partly an answer to that. In the kingdom Jesus describes, nobody negotiates their wage by the hour they arrived.
Anyone who identifies with the dawn workers feels the unfairness in their bones, and that is where the parable does its work. It does not ask you to find equal pay fair. It asks you to notice what happens inside when grace given to someone else feels like something taken from you. And the last-hour workers had not been idle out of laziness: "Because no one has hired us" (Matthew 20:7).
Walking with Jesus has a collection called The Parables of Jesus that takes them one a day — each with the question he was answering, a short reflection, a prayer, and one thing to carry into the day.
It is a one-time purchase, about five minutes a morning, and it never asks you to catch up on days you missed.