It has been years since I read this, so this will be short. When I read it again, I'll rewrite this.
This is one of those inevitable sequels. Basil of Baker Street was amazing. This is...eh. Indian mice, cliche plot twists, little character development; this book is one more example of why children's series are not often thought highly of. My other issue with these sequels is that they are little more than travelogues to 'strange' places which seems in the author's mind to equate with exciting. Let me explain something important. It's not!
If you are reading the series, read it. But I was not very impressed with this one.