Fresh from expediting a Rescue on the Oregon Trail (2015), Ranger golden retriever and trained rescue dog ain plunges into the past for a dog's-eye view of another era. Carried back by a magical first-aid kit, he lands in Rome's Colosseum, where he hooks up with young slave Marcus Cassius and Quintus Flavius, a new gladiator who is having second thoughts about his chosen profession. As it turns out, there's plenty of work for a rescue dog. Not only is Marcus attacked by a captive lion but Quintus goes temporarily AWOL from gladiator school and has to be tracked down. Along with posing handsomely in the scattered illustrations, Ranger (not anthropomorphized, though an occasional POV character) helps both of his new friends earn their freedom before returning home. Limiting violence to a few slashes and oblique references to "wild animal fights and executions," Messner tucks light doses of information about ancient Roman society and gladiatorial combat into both the plot and also a closing note kitted out with photographs and a bibliography. History, happy endings, and a heroic, time-traveling dog. What's not to like?