Sarah Smith 
The Vanished Child [EPUB ebook] 

‘Someone killed Richard. Now Richard wants to know why.’
New England, 1887. The millionaire William Knight is brutally murdered. His grandson, Richard, the only witness, is shocked into silence, then disappears, presumed kidnapped and killed.
Switzerland, 1905. Alexander von Reisden, ‘intellectual, immoral, and unstable, ‘ is ‘recognized’ as Richard. Despite Reisden’s insistence he’s not Richard, he is drawn into the affairs of the Knight family–gaining the hatred of the new heir and the friendship of the heir’s young fiancee, Perdita Halley.
But as Reisden tries to find out why Richard died, he begins to have unsettling feelings of familiarity. For he is a man without memory of his own childhood, and his obsession with finding Richard is leading him closer to a shattering truth.
And to a killer, still at large…