Improbable Labrador. The Improbable Empire, #7

Improbable Labrador(The Improbable Empire, Book 7) Centuries ago, a world-shattering cataclysm struck in the 15th century, devastating similar Earths in multiple timelines. Discovered by daring time travelers in the first volume of the series, Ox and Snake began the Improbable Empire to save their own Earth and others. The mission to rescue doomed populations has grown from desperate rescues into a sprawling, high-stakes operation spanning realities.
Louis, a reluctant recruit pulled into the fray by his formidable sister Adelhaide, never asked to become a hero. Yet when he's rescued from the apocalypse it has an effect. He rises swiftly through the ranks-from officer to commander of his own daring expedition, and must confront the relentless need to explain the multiverse to skeptical locals before he can save them. Along the way, he encounters versions of his own family and fights to save them without unraveling the fragile threads holding families and reality together.