Let me know if a hint is needed.
Hint two...Something happens that is very upsetting to Mac.
Not really sure, but I'd guess for "Widowmaker", although I was confused when you mention that this female friend of Mac's , has been appeared in two episodes. Now that I'm thinking about it, I have a second guess, if I'm allowed to do that. So, maybe it is "Ghost Ship", cause I thought that the female actor who appears in that episode, she has also appeared in another episode, (the one with the car races).
"Widowmaker" is correct. We meet Mike in "Jack of Lies" even though she is played by a different actress. What Mac is referring to seeing is a foothold on the rock face that he is having trouble reaching.