Yeah, we've been getting a few reports of book 1 rerendered being incompatible with chapter 20. If you haven't deleted Book 1 yet. follow these steps:
Save it when it says the last line "what now" in book 1, Then go to your File manager >device storage> android> data> com.adroid.mtwy > files > select the whole 'saves' folder and copy/move it to any other folder, after that uninstall book 1 , then install book 2, after installation go to file manager copy the 'saves' files and go to the same - device storage> android> data> com.adroid.mtwy > files and paste it there, then try start the game directly.