This reference, at Many Books dot net, is common on the Internet, including at Wikipedia:
The Man in Lower Ten
by Mary Roberts Rinehart
English, published in 1909
65,298 words (180 pages)
No. 1 in the Cornelia Van Gorder series
But there’s no such character in this excellent mystery novel, also dated 1906 in Wikipedia and elsewhere.
Caveat lector.
Blithe Spirit 