A Perilous Journey of Danger and Mayhem enters its final leg in this trilogy closer.After The Treacherous Seas (2019), Molly Pepper; her inventor mother, Cassandra; her best friend, Emmett; Emmett's long-lost-but-recently-found father, Capt. Wendell Lee; and sentient robot Robot are headed back to America. They face an assuredly bad reception, with three out of the five wanted fugitives, the captain a legal citizen but unable to prove it under the racist climate of the Chinese Exclusion Act, and Robot arguably someone else's property. In between the wacky hijinks of sneaking into the country and evading arrest, tension arises from Molly's and Emmett's uncertainty about whether his family reunion spells their imminent separation. The kids are prompted into action in the second act when a clue in a newspaper reveals their nemesis, Ambrose Rector, is back and planning something big. Parental reluctance to get involved leads to Molly, Emmett, and Robot's sneaking off to Washington, D.C., to thwart Rector (which requires first figuring out his plan) and includes a delightful heist at the Smithsonian and tracking down the Mothers of Invention. Reversals and betrayals open the final act of the story. Despite his silliness and tendency toward monologue, Rector's an effective villain because he plausibly stays a step ahead of the heroes and even makes good points during the final showdown. The alternate-history epilogue dazzles. Emmett and his father are Chinese; most other characters default to White.A fitting farewell packed with action, humor, and heart. (afterword) (Historical fantasy. 8-14)