Threshold

The second book in the popular Boundary SF adventure series co-authored by multiple New York Times bestseller Eric Flint and Ryk E. Spoor. 

When the strange fossil she'd discovered gave 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’re married to an overconfident super-sensor expert for the only private agency in space – the Ares Corporation – and your best friend is a former secret agent for the Interplanetary Research Institute of the United Nations, there's always somewhere farther to go. 

Soon Helen’s new discoveries will lead her  to the mysterious asteroid Ceres and beyond in a desperate race to reach Jupiter's perilous miniature system of radiation-bombarded moons. It seems the next gold rush is on–for alien technology.   

And there are people willing to do anything to get it – even if they must start the Solar System’s first interplanetary war!

Praise for the Boundary series:
“A genial, fast-paced sci-fi espionage thriller [that is] light in tone and hard on science…” –Publishers Weekly on Threshold

Eric Flint was the creator of the New York Times best-selling Ring of Fire series, the best-selling alternate history series of all time. Beginning with 1632, Flint—along with dozens of cowriters—chronicled what happened when the 20th-century town of Grantville, West Virginia, was transported through time and space to 17th-century Europe. In addition, Flint was the author, with New York Times best seller David Weber, of the Crown of Slaves Saga, as well as the Belisarius series with best-selling author David Drake. Flint was the editor of Jim Baen’s Universe, as well as numerous short story anthologies. Before becoming a writer, Flint worked as a trade union organizer, longshoreman, truck driver, auto worker, steel worker, oil worker, meatpacker, glassblower, and machinist. Eric Flint passed away in 2022.

Ryk E. Spoor, while earning his masters degree in Pittsburgh, became a playtesting consultant and writer for the Wizards of the Coast, the leading publisher of role-playing games and related novels. He now lives in East Greenbush, NY, working as a technical proposal writer for a high-tech R&D firm, and spending his non-writer time with his wife and sons. Spoor is the coauthor with New York Times best seller Eric Flint, of the popular Threshold series of science fiction novels. Spoor's solo novels for Baen include Paradigms Lost, Grand Central Arena, and Spheres of Influence. He is also the author of epic fantasy Phoenix Rising.