Berkley X1587 (1968)

Synopsis:

Sailing from England to America with a writer friend, Philip Knox, Dr. Gideon Fell, that eminent crime solver, encounters some odd characters, who are fated to have a volcanic effect on his stay in the U.S.  Prominent among them is the imperious Lady Tiverton (the former actress, Margery Vane), her latest young lover, and her longtime female companion.

All wind up at a dress rehearsal in a Connecticut theater endowed by Miss Vane. Murder stops the show, but provides Dr. Fell with a superb opportunity to display his own singular talents.