Detective William Somerset (Morgan Freeman)’s Timeline and Summary

Detective Somerset, who just wants to retire, gets saddled with a new partner in his last week: Detective Mills.
He gets Mills taken off their first murder case but soon learns that Mills' second case is connected with it. They have a serial killer on their hands.
Somerset realizes the killer is acting in accordance with the seven deadly sins, so he does some research at the library.
While following clues and uncovering new murders, Somerset forms a small friendship with Mills' wife, Tracy, who hates the city as much as he does.
She confesses to Somerset that she's pregnant, but she doesn't want to raise a child in the city.
He admits that he once had a partner who got pregnant, and he told her he wanted her to get an abortion. He knows he made the right decision, but he still regrets it. It's the saddest breakfast chat ever.
Eventually, the killer turns himself in but leads Mills and Somerset into the desert where the last two victims are.
There's no one there. But, a delivery truck shows up and gives Somerset a box.
Somerset opens it. It's Tracy's head.
He runs back to Mills and tries to get him to walk away, but Doe tells Mills that he killed his wife and unborn baby. Mills kills Doe.
Somerset is last seen talking to the captain and saying, in voice-over, that he believes the world is worth fighting for.