Audiobook narrated by Katy Sobey.
Sophie, Freddie, Hugo and Charlotte are separated from Shorten and Baby Bella due to the whim of Janus, the god-like AI entity that controls the time travelling ship they've been using. There is another ship, but it's more dangerous to travel on - and at least one iteration of their group (from another universe) has died on it already. They determine to go to ancient Rome to get (steal) the device that will control Janus, revert him to factory settings and remove his sentience. The device looks like a walking stick but it's so much more. They spend most of the book going from near-miss to near-miss as several iterations of evil HG Wells tries to kill them on Janus' behalf. In the end they fail in their mission and Bella is just as far away as before. I found the Roman adventure somwhat pointless - a lot of running around for no result, and I'm starting to think this series has gone on for too long. The first three Shorten books were tighter and more to the point. But there's only one more book, so... onward.