Part 3 Walkthrough – Here is a mission-by-mission walkthrough for Part III. It does not cover scenes between missions which are mostly informative, provide character development opportunities, and social interaction with other survivors.
Click on the link to the specific mission:
Part 4 Walkthrough – This walkthrough provides details on each phase of Part IV: Survival and contains many spoilers. You may wish to play through it first before using this walkthrough.
Each chapter is described with the best options to reach goals to increase your chance at survival, improve your character, and find other survivors.