J.I.M. Stewart 
Andrew and Tobias [PDF ebook] 

The Feltons are a family with a long lineage stretching back beyond the Norman Conquest. They now have a daughter, Ianthe, but prior to her birth Tobias, or Toby, was fostered and then adopted as their heir after he had miraculously survived the sinking of a refugee ship by a German U-Boat. Then, someone who is clearly Toby’s twin turns up as an under-gardener. He had been fostered by a Scottish couple, now dead. There is now general and disturbed confusion on everyone’s part – including the boys themselves. Stewart explores magnificently the nature of the complicated relationships, including those from outside of the family such as Toby’s lover; the irony of the situation; and the many ramifications of class and culture in the absurd situation the characters find themselves.