Raahhhhh I hated this episode.
I mean, I had to go out, find a forum, create a profile, and log in just to whinge about it!!
If they needed a paradox so badly, why didnt the Doctor just send Rivers book back, with the inscription “Dont go for coffee godammit!!! You will be eaten by angels!!!”
Or why did they just not send the book back at all? That way none of it would have happened.