Note: some minor spoilers ahead.
While not a direct sequel to Lotz’s previous novel The Three, Day Four does take place in the same timeline, one where the mysterious crash of four airliners on the same day and the decidedly weird doings of the three (or was it four?) child survivors leads to talk of the Apocalypse being on its way and the election of a deeply religious President in the U.S., one who oversees an extremely conservative federal government that seems to be doomsday preppers writ large. And official.
Day Four references the plane crashes, survivors and spookier stuff while sidestepping talk of the political landscape. The main story is largely self-contained, though, so reading The Three is not a prerequisite.
One might glibly describe Day Four as The Love Boat from Hell–and you would actually not be far off. As the story begins, the first three days of a cruise on The Beautiful Dreamer, of the fictitious Foveros Cruise Line, encounters nothing out of the ordinary after leaving Miami. On the fourth day it runs into mechanical problems. Then virus problems, rapist/murder problems, why-isn’t-anyone-coming-to-help problems and finally, possible ghost and maybe worse-than-that problems.
Lotz does an excellent job of ramping up the tension as conditions on the ship deteriorate, switching between a large cast of characters with the same ease she demonstrated in The Three. The crew of the ship is split into cabals and cliques, divided along lines of rank as well as ethnicity, each group typically speaking in their native tongue to better exclude others from the conversation. Even with the cruise running optimally it’s clear a lot of the people on board are never going to get along. And there are enough skeletons to fill a walk-in closet.
The passengers are a quirky mix of gossip bloggers, psychics, tourists and suicides-in-waiting. As things go sideways (literally, as the days without rescue go on) clashes among the passengers and crew increase. The power goes out. Toilets stop working. Ghosts start working.
To say more would be to enter into major spoiler territory but suffice to say the ending seems very much to set up another book, though whether it will follow the characters of Day Four or not is unclear (though I lean toward no). What is clear is that the people that inhabit this alternate present-day timeline are likely in for a bumpy few years.
If you approach Day Four on its own, the references to The Three may feel a bit oblique and the ending may be less satisfying but I still feel it works well on its own. As a companion to The Three, Lotz has crafted a nightmare cruise that neatly sets up even worse things to come. Recommended.