When Harrow dropped the book during his cancelled hit on the third man the sheet of paper (showing she is in debt bigtime) his sister had accidentally left in it must have fallen out. She's in the financial shits because of their father dying, getting pregnant then her new husband dying.
Harrow told the third man he had been paid by someone he met on a train to kill the three of them at $1,000 each. That doesn't really make any sense though, what kind of conversation on a train leads one person to trust another enough to ask him to carry out hits for them?!
The chap making the call at the end had killed the third man and had found said piece of paper when going through the office. It's not the actual bloke from the train as even with the shitty old phone network he would have recognised his distinctive voice.
We are still in the midst of a mystery. Did he really get the job from a random train passenger? Why is someone else hunting down at least one of the same targets and wants to meet Harrow? Add in the plot thread that basically Harrow is almost at the mental breakdown we've seen coming since the first time we saw the scrapbook way back in the past and it's probably a bad time for Harrow to be reforming his lifestyle if he's going to have a knock on the door very soon.
Then again someone killing his pregnant sister would probably turn him completely into a 1920s Terminator!
Christ that was a lot of words over a small detail, sorry >.<
Edit: VVV At least the jpg title told me what film that was, never seen it!