It's quite difficult to understand exactly what she means at first. This is written in a very oblique way, like a string of thoughts in a very particular voice. However I can give you what I understood from reading it; I think you have to look at it within the whole paragraph, the sentence isn't clear by itself. In the passage, the secretary is thinking about the dead man and how she is still attached to him. She talks about how she still finds a connection to him through the small books (his diaries.) Then she is musing about why she keeps reading them/typing them up- is she like a lovesick gir, still mourning him? is it because she takes comfort in old routines and feels better if she can imagine she's still helping him somehow? --Now we come to your sentence. Let's break it down, considering the above. Even if that’s so = even if those are the reasons in the middle of all = during the task/ after I began doing this task the story worked itself ahead of the man = the stories themselves became a motivation, not just the attachment to the memory of Mr Shepard. I will say Mr. Shepherd persuaded me, against his own will. = Her memories of him and his words in the books have motivated her to do this task, although he never told her to/ may not have wanted her to. (Private diaries? They were employer-secretary but she seems to have a deeper attachment to him than professional. I haven't read this book.) That's the best I can do. Hope it helps!

Thank you all the same, Randy.

It's too whimsical to get a handle on.