Imprudence

The Spotted Custard is repeatedly attacked by mysterious assailants, initially in London, and then when it is forced to take an expedition to Africa. The secret as to why this happening is maintained effectively, with plenty of red herrings along the way, and there's also some fun world-building as the story once again ventures further than the original tetralogy did.

Despite being a different series (due to the differing viewpoint character) there are plenty of ties with those earlier books, too, and it likely helps a lot to have read those, as well as the previous Custard Protocol instalment. In many ways, it's more obviously a direct sequel to The Parasol Protectorate, with some key characters from the previous generation returning to play an important role here.

It's perhaps also worth noting that this book is a little steamier than its predecessors. Of course, romance has always been a key element of the books, and sexuality has been a part of that, but Prudence's explorations here are a little more obvious here. (Having said which, the details may be quite heavily implied, but they aren't really explicit). There's also a subplot with Prim getting engaged for reasons that made perfect sense to Victorians, but don't to us, and it'll be fun to see where that goes in the next two books.

Not the strongest in the series, perhaps, largely due to Quesnel having little chemistry with Prudence - as I say, Prim's subplot is more interesting than what's supposed to be the main one. But it's full of the usual wit and charm, which is certainly good enough.