We picked up this paranormal detective series at the library, after a recent re-release with the new cover art. My son and daughter devoured them.
The context: Darkus' father, a private-detective in London who veers toward the paranormal for explanations of weird events, has been in a coma for four years. Darkus reads his father's case files to feel closer to him, while he's sleeping, and learns the family business. Then his father wakes, and they're on the hunt for a shadowy, paranormal group called The Combination.
Each mystery is a bit different, with a slight twist at the end that could be explained rationally or could be paranormal. We really enjoyed the second book, K-9, but I won't say exactly why...it would spoil the read! This book has a particularly dark tone, and if your MG reader is sensitive about dogs, I'd skip it.
The third one is set in LA and the desert southwest, where Darkus and his Dad meet their American "clones," or close enough to it, track The Combination to Area 51, and end up in Las Vegas, where his father ends up in a coma, again.