Look through the code line by line

This legacy code base is a beast, but hey, it’s your full time job and no one gave you a timeline for fixing this thing. You begin going through it function by function, line by line, looking for some obvious error. You wade through a sea of ambiguous comments and oddly labeled functions. Some functions appear to point to more nested functions in more nested folders; one more deep than the last. You just spent a few hours and have only scratched the surface. What do you do?

1. Continue looking through the code line by line
2. Google the Error
3. Strategically add a bunch of debug logging print statements
4. Ask the guy who wrote the code
5. Try running the code again