In South Africa, astronomer Sven Bronson discovers a pair of rogue planets speeding towards the solar system from the depths of interstellar space. The smaller Bronson Beta will enter a stable orbit around the Sun, but the gas giant Bronson Alpha will cause apocalyptic damage to the Earth through its gravitational influence, swing around the Sun, and finish off ol' Terra by smashing into it on its way out. It looks like humanity is doomed. But if "The League of the Last Days" can cross the gulf of space between Earth and Bronson Beta, some small fraction of the human race might just survive...
...and naturally, they do, since the sequel, After Worlds Collide, was also serialized between November 1933 and April 1934.
There was also a syndicated newspaper comic strip, Speed Spaulding, that loosely followed the plot of the first novel; it ran from January 1940 to March 1941.
The first novel included the following tropes:
- Apocalypse How: Bronson Alpha's first approach causes planetary societal collapse through massive tidal waves, earthquakes and volcanic activity. It wipes out the planet entirely on its second pass.
- America Saves the Day: Zig-zagged. The US government does a magnificent job of moving people and resources away from the vulnerable coasts; unfortunately, the devastation from Bronson Alpha's first pass is so comprehensive that the President can only radio his good wishes to the League from his devastated Midwestern redoubt, and wait for the second pass to finish off the planet.
- Artistic License Physics: The novel relates how during the first pass of Bronson Alpha and Bronson Beta, Bronson Alpha passed closed enough to collide with and destroy the moon. Several times during book, Bronson Alpha was clearly stated to be a gas giant as large as Jupiter. In reality, a gas giant that size passing close enough to earth to destroy the moon would have torn the earth to shreds with its gravity alone, no collision would have been needed.
- Disaster Scavengers: People are picking through abandoned New York City even as the streets flood due to Bronson Alpha's tidal effects.
- Egopolis: The encroaching planets are called Bronson Alpha and Bronson Beta after the scientist who discovers them.
- French Jerk: Professor Duquesne, although maybe that's the type of person you need to be to decide your own countrymen's efforts are doomed to failure and cross the Atlantic and half a continent in order to arrive at the Ark thirty minutes before it launches.
- Hope Spot: As the first Ark views the impending collision of Earth with Bronson Alpha, they briefly think it may only suffer a glancing blow and survive. They quickly learn that when you're talking planets, a glancing blow is quant. suff.
- I Love Nuclear Power
- Love Triangle: Between Dave Randsell, Tony Drake, and Eve Hendron.
- Missing Mom: Eve Hendron's mother is never mentioned.
- Next Sunday A.D.: The story takes place "in the middle third of the twentieth century", which would qualify for a book written in 1932.
- Noah's Story Arc: A pair of rogue planets are on a direct path to hit Earth. Scientists and governments rush to make a pair of rocket ships to hold the best of the best (and supplies) to send to another planet so humanity won't be extinguished.
- No Plans, No Prototype, No Backup: Averted; the League of the Last Days launches several test vehicles to try out their atomic engines, and when they complete the first Ark early, they immediately start work on a second, larger one for the rest of the construction team. In addition, other countries are building their own ships.
- Phlebotinum Breakdown: Without the Unobtanium available to the US team, the atomic engines of the French Ark melt down in mid-flight and it crashes back to Earth.
- Saintly Church: As society crumbles, Tony is aided in burying his mother by a kindly pair of clergymen (and the older man's wife), all of whom politely decline his offer to get them seats on the rocket.
- The Ark: At least five of them - two American, one British, one (failed) French, and one Japanese/Russian/German cooperative effort.
- 2-D Space: Semi-averted; the Bronson bodies approach the solar system from below the ecliptic. However, when Bronson Beta settles into its new orbit, it seems to be in more-or-less the same plane as the rest of the planets.
- Unobtainium: The massive tectonic disruptions from Bronson's first pass force a seam of exotic metal from the deep mantle all the way to the surface; it just happens to be exactly what the League needs to line the Ark's engine tubes.
- Weaponized Exhaust: When a crazed army of survivors attacks the Ark construction site, things look bleak until Randsell starts up the almost-complete first Ark, sets the engine to "1 G", and floats over the attacking hordes in blowtorch mode.
- Weird Moon: The Moon's orbit is severely altered by Bronson Alpha before it is ultimately destroyed.
The second novel included the following tropes:
- After the End
- Alien Sky: The atmosphere of Bronson Beta contains a higher proportion of noble gases (including neon) than Earth's; consequentially, there are often spectacular aurorae at night. In addition, the daytime sky is blue-green; it is later discovered that this is caused by algae that float into the sky as spores, develop miniature hydrogen balloons, and eventually fall back to the surface as "green rain".
- Ancient Tomb: Averted; after all, the Vanished People vanished.
- Apocalypse How: Bronson Beta was also a victim of planetary depopulation, since it held a thriving civilization before it was ejected out of its own solar system by Alpha and its original star.
- Apocalyptic Log: After the survivors move into one of the cities, they find written records from the Vanished People that describe the centuries between their discovery that a star was heading for them and its arrival. Apparently they voluntarily reduced their population over time, but their ultimate fate is unrevealed.
- Becoming the Mask: Kyto came to the US as a secret agent for Imperial Japan but learned to love its culture and eventually revealed the Dominion's plan to build their own Ark.
- Call a Smeerp a "Rabbit": One of the biologists comes up with elaborate scientific names for the native life, but eventually they just name them after their closest Earthly analogues.
- Commie Nazis: The Dominion of Asian Realists, a group of "fanatical Japanese, Russians and 'certain Germans'" who built their own ship in Manchuria and made it to Bronson Beta.
- Curb-Stomp Battle: After the Dominion sleep-gasses the second Ark's settlement, they fly in troop transports to occupy it and enslave the people. Unfortunately for them, people from the first Ark show up beforehand, find a warning message left by one of the locals, and rig a Ray Gun out of the Ark's atomic engines. They burn every one of the Dominion's flyers out of the sky.
- Domed Hometown: The cities of the Vanished People.
- Harmless Freezing: The entire biosphere of Bronson Beta seems to come back to life without any problem after it thaws out under the influence of the Sun; in addition, the domed cities and all the equipment, food, and machinery within them are just fine.
- Human Aliens: While exploring the city of the Vanished People/Million Years Dead, they find a picture of one on a wall. She looks perfectly human. Later video and audio recordings confirm this trope. Their clothes fit the humans, but the shoes don't quite work.
- Informed Flaw: Stowaway Marian Jackson is described as an empty-headed moron by multiple characters, but her actions and dialogue make her seem like a woman of slightly above average intelligence.
- Instant Sedation: One of the people from the second Ark's settlement barely has time to write a warning note about the Dominion's sleep gas attack before they fall unconscious.
- No Biochemical Barriers: Soon after arrival, a mysterious disease sweeps through the first Ark's people that sickens many and causes a couple of deaths. Later on, the find that the massive stockpiles of grains and meats they discover in the domed cities are perfectly edible. (Well, mostly.)
- Passing the Torch: The chapter is even titled "Tony, I pass the torch to you!"
- Ragnarök Proofing: The cities are not only still in pristine shape, but repair themselves.
- Reports of My Death Were Greatly Exaggerated: Dr. Dodson turns up alive, having been nursed back to health (minus an arm) after being wounded in the riots and Left for Dead in the first book.
- Science Fiction World Map: The book includes a chart of the rearranged solar system and a map of the Arks' landing area on Bronson Beta.
- Sequel Hook: The book leaves open the possibility that the Vanished People may reappear (did they die off, fly off into space or go into cryogenic suspension somewhere?), but no third book was produced. (Not by the original authors, at any rate. There is an unauthorized "sequel" published in 2011 which is, by most accounts, pretty bad.)
- Show Some Leg: a ploy suggested by two of the female colonists for infiltrating the bad guys' stronghold and successfully perpetrated by one of them.
- Uncertain Doom: In addition to the four rockets confirmed to have made it to Bronson Beta and the doomed French rocket, the first book mentions that China, South Africa, Australia, Argentina, and Italy are all working on evacuation rockets. Dr. Hendron estimates that a total of five rockets would probably survive, but none of the others appear on Bronson Beta. While the heroes speculate they were all destroyed, some of them might have made it and simply landed too far away to be immediately detected.