Skylark DuQuesne. Skylark Book 4

Scientists Dick Seaton and Marc DuQuesne were the deadliest enemies in the galaxy. Their feud had blazed among the stars and challenged the history of a thousand planets. But now a threat from outside the galaxy drove them into a desperate alliance as hordes of strange aliens stormed through space on a collision course with Man. Seaton and DuQuesne fought side by side to fend off the invasion - as Seaton kept constant, perilous watch for DuQuesne's inevitable double-cross.