Threshold

When the strange fossil she'd discovered had ended up giving her a trip to Mars, Helen Sutter thought she'd gone about as far as any paleontologist would ever go in her lifetime. But when you've also married A.J. Baker, overconfident super- sensor expert for the only private agency in space--the Ares Corporation--and your best friend Madeline Fathom Buckley is a former secret agent who's just signed on as the chief of security for the newly created and already embattled Interplanetary Resea...