The party was initially given a copy of the book by Delia Morrison although other copies were later found during their investigations.

Also known as 'The Walker by the Lake', this book was written by Alexander Roby and published, in 1923, by Whitehall Press, a vanity publisher. The book is bound in all-white cloth, blank cover and spine. The title page gives the title, in German and English, the author's initials 'A R' and a quote from Coleridge - Suppression Prepares for Overflow.

Neither narrative, nor poetry, nor drama, the book is nonetheless fascinating reading, with the text is split into halves headed 'First Act' and 'Second Act' and describes the dreams of an unnamed man, in the form of a case history. The dreams themselves are all recounted in German, though the rest of the text is in English. It seems a fair guess that the book is in some way autobiographical.

The dreams relate to a power that the dreamer slowly comes to know, a power he refers to as 'The King', 'Kaiwan' or 'the Unspeakable One'. Eventually he visits the city of Carcosa, a place of beauty and contentment.

It is from this book that Doctor Lionel Trollope was reading, Roby reciting the text alongside him, when he had a vision of his own death, a vision that proved accurate.

Nathaniel Browne lent the investigators' first copy of the book to Talbot Estus, who burned it on the night of his suicide.