{"schema_version":"bf_book_companion_v1","release_id":"20260406T231758Z","book":{"amazon_purchase_url":"https://www.amazon.com/dp/B00CBDC7OQ?tag=bookfrontier-20","asin":"B00CBDC7OQ","authors":["Marion Zimmer Bradley"],"book_id":"9781625589231","canonical_url":"https://bookfrontier.com/books/9781625589231","cover_image_url":"https://img.bookfrontier.com/9781625589231.jpg?v=20260406T231758Z%3A2026-04-06T23%3A17%3A58Z","description":"... across half a Galaxy, the Terran Empire maintains its sovereignty with the consent of the governed. It is a peaceful reign, held by compact and not by conquest. Again and again, when rebellion threatens the Terran Peace, the natives of the rebellious world have turned against their own people and sided with the men of Terra; not from fear, but from a sense of dedication. There has never been open war. The battle for these worlds is fought in the minds of a few men who stand between worlds; bound to one world by interest, loyalties, and allegiance; bound to the other by love. Such a world is Wolf. Such a man was Race Cargill of the Terran Secret Service.","forthcoming":false,"isbn13":"9781625589231","publication_date":"20130326","publisher":"Start Publishing LLC","slug":"the-door-through-space","subtitle":"Kindle Edition","title":"The Door Through Space"},"discovery":{"categories":{"all":[{"bisac_code":"FIC028030","confidence_band":"medium","label":"Space Opera","score":0.847,"source":"bisac_hint_model"},{"bisac_code":"FIC028050","confidence_band":"medium","label":"Military Sci-Fi","score":0.8446,"source":"bisac_hint_model"},{"bisac_code":"FIC028010","confidence_band":"medium","label":"Sci-Fi Adventure","score":0.8342,"source":"bisac_hint_model"}],"hint":[{"bisac_code":"FIC028030","confidence_band":"medium","label":"Space Opera","score":0.847,"source":"bisac_hint_model"},{"bisac_code":"FIC028050","confidence_band":"medium","label":"Military Sci-Fi","score":0.8446,"source":"bisac_hint_model"},{"bisac_code":"FIC028010","confidence_band":"medium","label":"Sci-Fi Adventure","score":0.8342,"source":"bisac_hint_model"}],"publisher":[{"bisac_code":"FIC009140","confidence_band":"high","label":"Military Fantasy","score":1,"source":"onix_publisher_code"},{"bisac_code":"FIC027220","confidence_band":"high","label":"Military Romance","score":1,"source":"onix_publisher_code"},{"bisac_code":"FIC028050","confidence_band":"high","label":"Military Sci-Fi","score":1,"source":"onix_publisher_code"}]},"genres":[{"label":"Space Opera","score":0.847,"slug":"space-opera"},{"label":"Military Sci-Fi","score":0.8446,"slug":"military-sci-fi"},{"label":"Sci-Fi Adventure","score":0.8342,"slug":"sci-fi-adventure"}],"reader_fit":["Good for readers who enjoy Space Opera","Good for readers interested in short stories","Good for fans of Science Fiction"],"related_lists":[{"intro":"","slug":"shelf-fic028030-science-fiction-space-opera","title":"Science Fiction Space Opera Books (fiction)","url":"https://bookfrontier.com/lists/shelf-fic028030-science-fiction-space-opera"},{"intro":"Big-canvas speculative stories where first contact drives the stakes.","slug":"between-the-shelves-space-opera-alien-contact","title":"Space Opera and Alien Contact Books","url":"https://bookfrontier.com/lists/between-the-shelves-space-opera-alien-contact"},{"intro":"","slug":"shelf-fic028050-science-fiction-military","title":"Science Fiction Military Books","url":"https://bookfrontier.com/lists/shelf-fic028050-science-fiction-military"}],"series":null,"similar_books":[{"authors":["E.E. \"Doc\" Smith"],"book_id":"9781649742308","cover_image_url":"https://img.bookfrontier.com/9781649742308.jpg?v=20260406T231758Z%3A2026-04-06T23%3A17%3A58Z","score":21.6659,"title":"Second Stage Lensman","url":"https://bookfrontier.com/books/9781649742308"},{"authors":["H. Beam Piper"],"book_id":"9781682999400","cover_image_url":"https://img.bookfrontier.com/9781682999400.jpg?v=20260406T231758Z%3A2026-04-06T23%3A17%3A58Z","score":19.6831,"title":"Ullr Uprising","url":"https://bookfrontier.com/books/9781682999400"},{"authors":["Harry Harrison"],"book_id":"9781681464947","cover_image_url":"https://img.bookfrontier.com/9781681464947.jpg?v=20260406T231758Z%3A2026-04-06T23%3A17%3A58Z","score":19.2984,"title":"The Stainless Steel Rat and the Misplaced Battleship","url":"https://bookfrontier.com/books/9781681464947"},{"authors":["Mike Resnick"],"book_id":"9781591026952","cover_image_url":"https://img.bookfrontier.com/9781591026952.jpg?v=20260406T231758Z%3A2026-04-06T23%3A17%3A58Z","score":19.0018,"title":"Starship: Rebel","url":"https://bookfrontier.com/books/9781591026952"},{"authors":["John Love"],"book_id":"9781597803915","cover_image_url":"https://img.bookfrontier.com/9781597803915.jpg?v=20260406T231758Z%3A2026-04-06T23%3A17%3A58Z","score":18.9192,"title":"Faith","url":"https://bookfrontier.com/books/9781597803915"},{"authors":["Keith Laumer"],"book_id":"9781625587329","cover_image_url":"https://img.bookfrontier.com/9781625587329.jpg?v=20260406T231758Z%3A2026-04-06T23%3A17%3A58Z","score":18.9076,"title":"Greylorn","url":"https://bookfrontier.com/books/9781625587329"},{"authors":["Neal Asher"],"book_id":"9781627933100","cover_image_url":"https://img.bookfrontier.com/9781627933100.jpg?v=20260406T231758Z%3A2026-04-06T23%3A17%3A58Z","score":18.9024,"title":"Prador Moon","url":"https://bookfrontier.com/books/9781627933100"},{"authors":["Clifford D. Simak"],"book_id":"9781649741912","cover_image_url":"https://img.bookfrontier.com/9781649741912.jpg?v=20260406T231758Z%3A2026-04-06T23%3A17%3A58Z","score":18.8389,"title":"Message From Mars","url":"https://bookfrontier.com/books/9781649741912"}],"topics":[{"evidence_refs":["keyword:military science fiction"],"label":"Science","score":0.2945,"slug":"science"},{"evidence_refs":["keyword:military science fiction"],"label":"Military","score":0.1382,"slug":"military"},{"evidence_refs":["phrase_map_match"],"label":"Short Stories","score":0.0624,"slug":"short-story"},{"evidence_refs":["keyword:space espionage romance"],"label":"Space","score":0.0595,"slug":"space"}],"what_you_get":["Themes: Science, Military, Short Stories.","Reading lane: Space Opera and Military Sci Fi.","Publisher: Start Publishing LLC."]},"llm_signals":null,"source_presence":{"amazon":true,"book_detail":true,"goodreads":true,"llm_signals":false,"similarity_seed":true},"stats":{"amazon_ratings_count":0,"goodreads_ratings_count":948,"goodreads_reviews_count":102,"quality_score":0.905}}