Heart of a Mystery, The by L. T. Meade (1854 - 1914) and Robert Eustace (1854 - 1943)

The Heart of Mystery by L. T. Meade and Robert Eustace was published in 1901 in six installments in the Windsor Magazine, Vol. 14. The stories relate the adventures of a young Englishman summoned to the deathbed of an old friend in Paris who subsequently finds himself embroiled in a web of danger, espionage and intrigue. - Summary by J. M. Smallheer