A decent continuation of the series. It was enjoyable to read, but a little meh overall. Just how in this story Stig's big adventure to find and save his sister is played as a bit of a joke-- he travels for hours only to arrive back basically where he started and she was never in danger anyway-- there's a sort of emptiness to this story. Though it is presented as an adventure of Stig and Tilde, they actually do relatively little, instead benefiting from the preparations of those who came before; and the greatest adventure in this volume is actually someone else's story that they are told.
Another dissatisfaction for me: I suspect that the "wolf speech" encodes actual words; it should be simple because it appears to be just squiggly letters rotated to varying degrees, but it eluded me. There aren't enough passages to provide a clear starting point, nor enough to make the effort really worth it; and I'm not sure if the words would have been translated anyway, or left in the original French.