The Beacon to Elsewhere by James H. Schmitz

When a hard-edged Chief Commissioner learns that the mysterious compound Ym-400 has been stolen from an automatic freighter without tripping a single alarm, the case quickly stops looking like ordinary sabotage. Howard Camhorn and Gus Fry know the theft points to insiders, vast resources, and a secret so dangerous it could shift the balance of power across the interstellar civilization. Ym-400 is no simple explosive or fuel source: tied to unstable elements, Riemann-space effects, and a stabilizing agent called Ymir, it may control radioactivity, transmute space-time stresses, or unlock matter transmission. Yet the project has already cost more than a thousand lives in disastrous experiments, and even partial disclosure could alert enemies. Camhorn hopes rumor will deter the thieves long enough to buy time. But after months of dead ends, the trail leads to Terra, where IPA investigator Frank Dowland must pose as a game collector among suspicious Freeholder families. On Lion Mesa, he discovers the Trelawneys' hidden connection to the missing substance and to a machine for traveling back through time. Their plan is terrifyingly ambitious: use Ym-400 to create scientific bases in the past, return with advanced weapons, and overthrow Overgovernment control of Terra. As armed Troopers close in, Dowland faces a conspiracy that could rewrite history itself. This edition has been fully restored with modern typesetting, custom cover design.