Agents and editors want career writers, not one book wonders. I had already started A Baby's Bones, and was enjoying the story of Sage and her uncovering of the past, but I'm aware it probably wouldn't make a good second book for The Secrets of Life and Death. I've left Jack and Sadie bloodied and bruised, and they need to work out where they are going (and so do I). Writing a credible follow up (I hate sequels and trilogies) is sensible but I'm not sure how to go about it.
So I've looked around at second books that follow a strong first. Some of them are, frankly, a bit weak, especially those that are written as the middle of a trilogy. I loved Phillip Pullman's His Dark Materials trilogy but The Subtle Knife feels like the weakest to me. The novelty of the world building in the first book, Northern Lights, is over and the story is building to a big finish in The Amber Spyglass.
I feel a pressure to go even bigger than book 1, as if there has to be an escalation. I suppose unless I do sell a book, and the editors there suggest a direction, I'm in limbo, and I can carry on writing for myself. It's a rather nice feeling. In the meantime, Jack and Sadie seem to be working on a conundrum that might yet throw up the right antagonists. Otherwise the book is going to have to be called: Jack and Sadie go Gardening.