The boys are hired by Fenton Prentice, who seems to be experiencing a haunting in his apartment and whilst there, they get involved in a robbery. When it later comes to light that what was stolen, a crystal statue of The Carpathian Hound (the invisible dog of the title), belonged to Prentice, the boys have a bigger case to crack. Probably my favourite of the entire series, Carey perfectly captures the mood and atmosphere of the post-Christmas period and her sense of location here is superb - the park, the church and Paseo Place are all vividly described. The story zips along, from the superb opening sequence right through to the climax, with plenty of well-drawn characters and some excellent set pieces (including an encounter in the church). This also gains credit by having two supernatural events (an out-of-body wanderer and the cover-star phantom priest, the latter of which inspires the great last line) that are presented ‘just so’, with no attempt to explain them away. Rich, well paced and with a good mystery at its heart, this is an excellent book and very highly recommended.The 1979 edition (left) is the one I read and features my favourite cover. I got the 1981 edition (right) as that's the one most of my collection is in, though the cover isn't nearly as evocative for me.