New York: Street & Smith Corporation, Publishers. (1889). Ca 1898. Cf. Hubin I, p. 758, which gives the title as "Unknown; or, The Mystery of Raven Rocks." 224 pp. 12mo. 6-7/8" x 4-7/8" Printed wrappers, stapled. Spine roll. Paper chipping at spine ends, with largish chip from front panel top left. A VG copy. Item #32821
The rear wrapper makes reference to "conditions due to the war", which we presume to be the Spanish American War, corroborated by the preface, which refers to Mrs Southworth in the present tense.