Rails query through association limited to most recent record?

class User 
has_many :books

I need a query that returns:

Users whose most recent book has :complete => true. i.e. If a user's most recent book has :complete => false, I do not want them in my result.

What I have so far

User.joins(:books).merge(Book.where(:complete => true))

which is a promising start but does not give me the result I need. I've tried adding an .order("created_on desc").limit(1)
to the end of the above query but then I end up with only one result when I am expecting many.

Thanks!