The first of the Lensman novels by E.E. Smith, aka, E.E. ‘Doc’ Smith, Triplanetary never mentions Lensmen and you might not even know that it’s a series, except that the masterful, manly, monogamous, and magnificently named hero (Conway Costigan) is begging for more appearances.
Clearly the product of serialization, you can see where each installment began and ended. Pirates attack a space liner/cruise ship, but Costigan and Captain Bradley escape and lead a counterattack against the evil pirates. Then aliens appear and wipe out everyone but Bradley, Costigan, and a love interest. (Cliffhanger!) The escape from the aliens and send super technology info to Triplanetary, a space super spy/military agency, who finally and fully defeat the space pirates – but the aliens are back! (Cliffhanger!) Manly men in awesome space ships fight the aliens to a draw and peace is achieved.
Smith tries really hard to make his science believable by the standards of the day (he first wrote it in the thirties) and I’ll probably read more of these.