Answer:
Enigmatic - Save for one short, [mysterious] message left in
my mailbox on Christmas Eve, I have not heard
from him since his disappearance a year and a
half ago.
Prone - Many a stouthearted patriot has found himself
[lying face down] in the tangled bunting and
timbers of a smashed reviewing stand.
Bourgeois - At no time were his experiments, as Premier Slezak
called them, "a [characterized by materialistic pursuits
or concerns] plot to shackle the true democracies
of the world."
Dubiously - "Did you give it everything you had?" asked the
general [in a doubtful manner].