This is the beginning of a new series spun off
The Spiderwick Chronicles. The characters are new, the setting changed to Florida, but the concept is the same: we are surrounded by an unseen, mostly malevolent, world of magical creatures, and certain magical items (here a four-leaf clover and the water a nixie has swum in) can give one the Sight to see it.
While it doesn't have the freshness and exciting suspense of the original series, and Nick and Laurie are rather unlikable protagonists, it does have one bit that long-time fans will enjoy: an appearance in the story by the author, illustrator, and the twins on whom the series is supposedly based. Nick and Laurie go to see them at a book signing, hoping for some advice in dealing with a problem with a giant, and are vastly disappointed. The author has fun razzing herself and her partner, and it provides a little metafiction interlude that jazzes the proceedings up for a while. But in the next book the basic story will have to pick up considerably, and Nick and Laurie will have to become a whole lot more appealing, to hold onto fans of the original series.