The book centers on two siblings, Kendra and Seth Sorenson, who visit their grandfather's mansion, which unbeknownst to most of the world, is a reserve for mystical creatures.

Shortly afterward, Kendra follows a series of clues given to her by Stan, which leads her to an instruction to drink unpasteurized milk straight from the cow on the farm.

Stan also informs them that Midsummer's Eve is approaching, a festival night on which the boundaries containing magical entities dissolve.

Stan places Seth and Kendra in the attic, warning them not to leave their beds till morning.

Though Seth and Kendra are unharmed, the goblins provide entrance to other creatures, wreaking havoc in the house, turning Dale into a statue, and abducting Stan and Lena, the ex-naiad housekeeper.

Ruth tells Kendra and Seth that the Forgotten Chapel is actually a containment facility for one of the most powerful demons in existence, Bahumat.

The Queen spares Kendra's life, and provides her with instructions on how to create an elixir to enlarge the fairies and enhance their powers.

The enlarged fairies attack Bahumat and turn corrupted versions of themselves back to their original form.

Brandon Mull had wanted to become a fantasy novelist ever since reading The Chronicles of Narnia, The Lord of the Rings, and Harry Potter while growing up.

[1] As an adult working in the marketing field to support his family in Utah, he would secretly write fictional stories off-hours,[2][3] a hobby he had since he was teenager.

Various reviewers have favorably compared Fablehaven to the Harry Potter series, including author Orson Scott Card.

[18] Obert Skye, another author, found the world of Fablehaven to be creepy in some aspects, but inviting in others.

[19] Columbia Daily Tribune's Holly E. Newton wrote that the book is "so compelling and so well written" that readers will not be able to stop reading Fablehaven.

[20] Scott Iwasaki from Deseret News called the book "a quick-paced read" that successfully explores a fantasy world.

[10] In contrast, Kirkus Reviews criticized the book having Seth disobeying an adult being used as a frequent plot device, and stated that "[w]itty repartee between the central characters, as well as the occasional well-done set piece, isn't enough to hold this hefty debut together".

[21] Matt Berman of Common Sense Media similarly criticized the plot device and called the characters of Seth and Kendra "stereotypes".

[27] The potential of a film adaptation has been discussed, with the rights to one even being optioned a couple of times.