Your target is Jill Valentine, a S.T.A.R.S. operative. You'll begin in the residential areas of Raccoon City, which are now overrun with infected. The path to Jill will be fraught with danger, including new enemy types like Brain Suckers (fast, parasitic creatures) and more aggressive Lickers. Use your mini-map to track Jill's movements, as she will be actively trying to evade you.
You'll encounter various environmental puzzles, such as locked gates requiring power to be restored or debris blocking your path that needs to be cleared with explosives (Beltway is useful here). Expect ambushes from both infected and a few remaining RPD officers who are trying to protect Jill. She is a skilled combatant herself and will use cover and grenades. Do not underestimate her. The pursuit will lead you to a clock tower or a similar landmark.