How does Mark escape with Trina, Deedee, and Alec in Chapter 59?

Mark frees Deedee, and Trina then takes hold of Deedee to protect her. Mark then goes for Alec, who is fighting away. Terror breaks out when one of the infected begins shooting a Transvice, and the infected mob flees from the house. Mark, Trina, Alec, and Deedee race down the street.