in half-life 2, the player is gordon freeman (the same character as in half-life). it begins about 20 years after the first half-life. the combine, a group of evil aliens, took over earth and made humans their slaves. gordon freeman wakes up on a train in a place named city 17. he finds the resistance, some humans who fight the combine. in the game, he must help them and fight with them. the game ends with gordon freeman stopping doctor breen, the evil human who is helping the combine.