Firehand
by Andre Norton and P. M. Griffin
So how do you battle a powerful, time-traveling alien race who visited Earth in the far
distant past? Ross Murdock has the right idea: You go back in time yourself to set up a
resistance in the Dominion of Virgin civilization, which was wiped out by the murderous,
bald aliens. And you get yourself a love interest.
. . . she kissed him joyfully.
Firehand by Andre Norton and P.
M. Griffin (Tor Books, June 1994).