I was having a conversation today with someone who confessed to not knowing much about the history of the Church, but wanting to know more. I found myself very quickly recommending a book I haven't read for ages, but which is really good as a basic introduction. It's 600-odd pages, and is written by people who know what they're talking about, but looks like a modern school textbook and reads in a way that is very accessible to teenagers. On the other hand, it's 600-odd pages and covers 2000 years of history, so it's only a quick overview. But good for an introduction and seeing how everything fits together.