The series focuses on the arrival of a group of American soldiers to the parallel world described in Destroyermen in 1847 and their conflict with an insidious empire called the Holy Dominion, which controls a large chunk of what would be Mexico in our world. Along with the local tribes that resist the Dominion, the Americans will form a nation of their own, dedicated to the ideals they've left behind.
A primary focus is on Captain Lewis Cayce, an artilleryman who was on his way to join the Mexican-American War. The ships of the convoy suddenly find themselves caught up in a storm a few miles off the coast of the Yucatán Peninsula. Most of the ships end up crashing on land, seemingly falling from the sky. It's not long before the survivors begin to discover odd creatures populating the land that shouldn't be present anywhere on the Earth they know. They also run into a group of what appear to be Indians led by a catlike being calling herself Warmaster Varaa-Choon. Her people are called Mi-Anakka (those who've read the Destroyermen series will recognize them as the Lemurians). Varaa-Choon and some of the people she leads speak English and are able to communicate with the Americans. After a battle with lizardlike creatures called Grik, which seem to be allied with the Doms, the Americans are led by Varaa-Choon to the city of Uxmal, with Captain Cayce intending to build an army to defend Uxmal and the other city-states threatened by the Doms while espousing the ideals of the United States.
The series currently consists of three novels: Purgatory's Shore, Hell's March and Devil's Battle.
The series includes examples of the following tropes.
- Action Girl: Leonor Anson and Varaa-Choon.
- The Alliance: Cayce and De Russy's goal is to form an army to defend the city-states of Yucatán against the Doms and their allies. They pitch the idea to Alcalde Periz and the other alcaldes. However, only three of them (Periz, Ortiz, and Truro) show an immediate willingness to join and supply the new army. Their three cities (Uxmal, Pidra Blanca, and Itzincab) from what is starting to become known as the Three Cities Alliance.
- The Captain:
- Lewis Cayce begins the series as an artillery captain but is fairly quickly promoted to major and is made the commander-in-chief of the army.
- Giles Anson is a captain in the Texas Mounted Volunteers.
- Eric Holland is the only naval captain at the beginning. He is the master of the Mary Riggs. After the transition, which results in the Mary Riggs and many other ships ending up far inland, he's forced to watch as his ship is broken apart for parts. He eventually takes command of HMS Tiger, since the highest-ranking surviving officer on that ship is a lieutenant.
- Cat Folk: The Mi-Anakka are upright-walking catlike beings from a distant land. Of course, anyone familiar with the Destroyermen books will recognize them as Lemurians from Madagascar. The Mi-Anakka in Yucatán arrived there by ship and crash-landed (after being forced to run aground by Dom ships), finding themselves as lost as the Americans. These particular Lemurians were on a scouting mission for the Republic of Real People in Southern Africa, personally sent by the Caesar.
- Colonel Badass: Averted. Colonel Ruberdeau De Russy is a politician, not a soldier. Nevertheless, he's the highest-ranking officer among the survivors, which puts him in command. In a pinch, though, it's up to Captain Cayce to take command and repel the attack on the Americans from some hostile tribesmen and their Grik allies. Afterwards, De Russy admits his lack of combat and command experience and places overall military command onto Cayce's shoulders, promising not to interfere in any strictly military matter while himself acting in a political capacity. He hopes to eventually be able to lift the burden of command from Cayce's shoulders once he has enough experience.
- Easy Logistics: Averted hard. Since the people of Yucatán don't really have much of an industry, establishing the production of guns and ammunition is a serious hurdle early on. Even something as basic as paper (for paper cartridges) would require some serious adjustments, to say nothing of gunpowder (which they can already produce, but it's too crude for army purposes) and ammo for both fighting and training. Since the plan is to have both infantry and artillery, they also need to build more cannons than what made it to this world. Horses for cavalry are another issue. While they do exist on this world (brought over by some of the groups), the hostile nature of the peninsula means they don't run wild and are largely owned by wealthy natives. While Varaa-Choon suggests using the native armabuey to pull artillery pieces, Cayce explains that one of the main reasons the US Army was so successful in fighting the Mexicans was the high mobility of their "flying artillery", which requires horses for the cannons and the men instead of the slow armabuey. The only thing that's helpful in the beginning is the large supply of muskets the Americans have managed to salvage from the wrecks of their ships.
- The Elites Jump Ship: While it’s fairly understandable that all but a few of the mostly wealthy civilians on the Tiger feel more vulnerable than the soldiers and want to evacuate to safer territory, the ship they're on also abandons the soldiers still ashore after a while, although that is at least partially Colonel Wicklow's decision and not theirs. They end up blindly heading straight into Dom territory and end up tortured to death or sold into slavery.
- The Empire: The Holy Dominion (founded by the Spanish arrivals of a Manila galleon) rules over a significant chunk of what would be Mexico on our world. They're seeking to expand their control over Yucatán using local tribes friendly to them. Varaa-Choon also reveals the existence of the Empire of New Britain Isles.
- Enemy Mine: A small detachment of Mexican lancers led by Alférez (Ensign) Ramon Lara was transported to this other world along with the Americans. Recognizing the need to work together, Lara pledges his assistance as well as those of his men to the Americans. Not all Americans are pleased to be working side-by-side with those they've only recently called enemies. This is especially true of Captain Giles Anson and his daughter Leonor. Most of Anson's family was murdered by Mexican soldiers, while Leonor was raped. Naturally, she hates Mexican soldiers with a passion. While she recognizes that Lara had nothing to do with it, she has trouble reconciling who he is with what he is. Anson points out that it would've been a lot easier for Leonor to accept Lara and his men if they changed their uniforms (especially since physically the Mexicans don't look that much different from the Uxmalos), but Lara (now promoted to teniente - lieutenant) actually has the Uxmalos make more of them for his expanded lancer corps. He does invite Leonor to a dance during a ball, and Leonor actually accepts, if a little reluctantly.
- Famous Ancestor: It's heavily implied that Captain Giles Anson is the ancestor to Captain Samuel Anson from the main series.
- Hufflepuff House: Passengers or crewmen from four of the ships to come through the squall play pretty big roles, but the Xenophon leaves very few survivors, and those survivors are injured, taken to Uxmal for healing by the Lemurians, and then never mentioned again (at least in the first book).
- I Choose to Stay: After arriving to Uxmal, Cayce explains that only those willing will be a part of this new army. Anyone who wants to be discharged may leave but will have to hand in their weapons and leave. In the end, only three men leave and only because they feel they're too old to be proper drill sergeants for the new army. However, they express their desire to fight when the time comes. As such, Colonel De Russy suggests giving them a reservist status, letting them keep their weapons and uniforms.
- Lizard Folk: A number of Grik tribes are allied with the human tribes loyal to the Dominion. Varaa-Choon does point out, however, that these are not the "true Grik", like the ones that control most of Africa. They're a related species that they've taken to calling Grik due to their similarities.
- Love Interest: During their second ball in Uxmal, Samantha explains that she and Angelique need protection in this new world and have chosen to attach themselves to capable men. Angelique has chosen Colonel De Russy, as neither is made for combat. Meanwhile, Samantha wants a man of action rather than words and spends some time choosing between Cacey and Anson. She eventually settles on Anson after realizing that Leonor has fallen for Cacey and unwilling to fight a genuine Action Girl for him. Besides, she claims that Anson would be a catch even under normal circumstances.
- Painless Death for a Price: In "Hell's March", after Captain Cayce's army defeats a Dominion force that was in the process of massacring a village, he offers the surviving enemy soldiers a choice: either tell him what he wants to know Dominion troop movements, in which case he'll have them executed by firing squad, or remain silent, in which case he'll turn them over to the surviving villagers (who at that moment are already crucifying the Blood Priests who'd led the attack). All of the soldiers start talking at once. Subverted in that Cayce ends up sparing them after all, since it turns out they'd been Forced into Evil and would have been tortured to death had they refused to carry out their orders.
- Rape as Drama: Leonor was raped by Mexican soldiers the same day her mother and siblings were killed by them. Naturally, she hates Mexican soldiers with a passion, as does her father.
- Reasonable Authority Figure:
- Alcalde Ikan Periz is the ruler and war leader of Uxmal. He is the first to welcome the Americans and the first to get on board with their plan to form an army to protect the city-states from the Doms and their allies.
- The same could be said about Alcalde Ortiz from Pidra Blanca and Alcalde Truro from Itzincab.
- King Har-Kaaska is a Mi-Anakka in charge of the Ocelomeh. He admits that "king" is not an appropriate title, since he doesn't rule any lands or cities. But he had to call himself something. He is the leader of the Mi-Anakka who survived when their schooner was forced to run aground in Yucatán by Dom ships. He readily agrees to give his men to the Americans to be trained in their style of warfare, although he privately admits to Varaa-Choon that he doesn't see any way for them to defeat the Doms due to their great numbers and "infectious" faith.
- Religion of Evil: The version of Christianity practiced by the Doms has been horribly twisted and merged with the pagan beliefs of the local Mayincatec tribes. Suffering seems to be the central point of the Dom faith, with the belief that getting into Heaven requires physical torment. Human sacrifice is likewise practiced. While the Dom priesthood has hardly been pleasant, it's getting even worse with the blood priests, a radical new faction, gradually taking over.
- Royals Who Actually Do Something: Samantha Wilde and Angelique Mercure are among the wealthy European civilians who end up transported to this world on HMS Tiger. Unlike many of the others, they voluntarily choose to assist and care for the many wounded. In particular, Samantha is the daughter of a British vice-consul, although she points out that her father was a soldier. Not much is revealed about Angelique's history, but Samantha says that their fathers are business partners, so she seems to be highly placed in the French society (and since the transition happens during the July Monarchy, it's possible that she might be a member of the aristocracy).
- Ruling Couple: The wives of all alcaldes hold the title of "segunda alcaldesa" and are required to assume their husbands' duties in their absence (or death). It's understood the Alcalde Periz's wife Sira is his equal partner on a daily basis.
- Sweet Polly Oliver: Not long after meeting Captain Giles Anson's son Private Leon Anson, Cayce realizes that "Leon" is, in fact, a girl dressed as a young man so she could fight along her father. He eventually learns that her real name is Leonor. Most people figure it out soon after, either from observing "Leon" or when Captain Anson slips up and calls her "girl" during a battle. Eventually, Leonor expresses her desire to come to a ball dressed as a girl (in a gown loaned by Samantha) and escorted by Cayce.
- Trapped in Another World: The Americans learn from Varaa-Choon that they're on another Earth with no way back. This is no surprise to Varaa-Choon, who explains that many groups of people have ended up in this world. It's later revealed that she is from the Republic of Real People in Southern Africa. In fact, they have been aware of the existence of Americans since the arrival of a British ship in 1811.
- We ARE Struggling Together: There's a lot of conflict among the Americans over various divisions, from national origins (e.g. Irish vs British, American vs Mexican) to whether one is a regular or a volunteer.
