In story mode, instead of following the girl to the gang's hideout, at the beginning of the level, wait for the train to pass. Then, immediately jump on the back-most bottom support rail. Have the Terminal Uplink out and jump down. If done correctly, you should be in the streets with just a second or two before the cameras catch you. Then, dive in and out of cover as fast as you can, because you do not have to worry about the girl catching you (because she is behind you). When you get to the stairway to enter the sewers, do not go in. Instead, look for a crate in the far left corner. Hide behind this until the girl arrives. When she goes out of sight in the sewers, follow her as usual.