When Pegasus arrives at Gethsemane, they find a planet than only has a few days to live. A Rogue Planet has entered the system and will collide with Gethsemane in just a few days. (The planet was unleashed when its own star was destroyed by the Marauding Meta-Goths of Mensa during the Fifth Crusade).
Most of the planet has already evacuated via "Heaven's Gate," an enormous city-sized machine that Gethsemanites believe allows them to enter heaven directly without dying, and, in some cases, return. Commander Keeler is intrigued by the machine, and against the advice of Dead Keeler, travels through the machine hoping to meet his deceased wife Delia. Instead, he finds himself on an alternate Sapphire, one where he never left to command Pegasus, and where his wife didn't die.
Meanwhile, most of the crew takes an opportunity to enjoy shore leave on the doomed planet, even as groundquakes and tidal waves make the surface increasingly inhospitable, and the Rogue Planet looms ever larger in the heavens. Trajan Lear discovers a hidden tragedy. Children can not pass through Heaven's Gate. The Gethsemanites, knowing their fate, had virtually stopped reproducing, but there are still some 10,000 children under the age of 15 who will be doomed when the planet collides. Trajan Lear undertakes to rescue them and bring them to Pegasus,against the opposition of the colony's leader, who would rather see the children dead than raised in the strange ways of the Pegasus crew.
Finally, as the two worlds close in for their final collision, the Heaven's Gate swings outward, being not only a gate to Heaven, but a gate to Hell as well. Pegasus fights the largest battle of its journey against the horrible and nightmarish creatures that emerge from the gate not just in space, but on the ship itself.
When Chapter 02: Keeler's reference to 'twelve colonies' and a 'rag-tag fugitive fleet' is a reference to Battlestar Galactica.
- Chapter 01: What Keeler calls a "ziga" is actually a Zia sun symbol of the Zia Pueblo people.
- Chapter 01: Hildegard Kahn's tirades are almost word-for-word identical to tirades reportedly made by Hillary Rodham Clinton.
- Chapter 02: Bill Keeler references Dante's Inferno and Bill and Ted's Bogus Journey.
- Chapter 04: This is the second time Max Jordan and Johnny Rook have been involved in a shoot out in or near a shoe warehouse. The first time was in Book 06.
- Chapter 07: Delia Keeler's maiden name was Delia Katherine Anne Chanski, or Delia K.A. Chanski, an homage to Red Dwarf's Christine Kachanski.
- Chapter 07: Delia Keeler's books bear the titles of television soap operas.
- Chapter 10: One of the rescue scenarios is a riff on Children of the Corn .
- Chapter 10: Quattro-triticale is an obscure Star Trek reference.
- Chapter 10: "Crazy Purple Knock-Out Gas" is a Family Guy reference.
- Chapter 11: Most of the USNC professors in this scene have names that are close to or taken from the secret identities of superheroes including Superman, Batman, the Green Lantern, Spiderman, and the Shadow.
- Chapter 12: The names Shorpy and Soarboar were inspired by Shorpy: The 100 Year Old Photo Blog .
- Chapter 13: The constellations Keeler mentions are all names of Futurama characters
- Chapter 15: Some idiot stuck in an Airplane reference at a totally inappropriate juncture.
- Chapter 16: The trans-dimensional monster bears more than a passing resemblance to Cthulu.
- Chapter 17: The poem Eliza Jane Change recites is from MacBeth, Act 1, scene 1.