The Minor Transgression was a small Covenant missionary ship employed by the Ministry of Tranquility. It's task was to search the edges of Covenant space for Forerunner relics. The ship was captained by the Kig-Yar Ship Mistress Chur'R-Yar, "overseen" by the Unggoy Deacon Dadab, and maintained by the Huragok Lighter Than Some.
The ship was in empty space when an unidentified ship suddenly came out of slipspace in front of them. As the ship was of no Covenant design, the entire ship was put on high alert and weapons were readied. With precise point-laser weapons, the Transgression took out the unidentified ship's external sensors and communication devices. It then used it's on-board 'umbilical' to serve as a bridge between the two ships. While the Kig-Yar raided the freighter's supply of fruits, Dadab retrieved the computer for Lighter Than Some, who was able to recover the freighter's point of origin, a nearby planet.
When the Transgression arrived in the star system, their on-board luminary showed thousands of Forerunner relics nearby. The Kig-Yar disconnected the Luminary from the ship's communication relay to prevent it from transmitting a true account of how many relics the planet held. The Kig-Yar intended to take some artefacts for themselves and sell them for profit. On their way to the planet they encountered another freighter, of the same design, and the Luminary showed that the freighter contained one Forerunner relic. Eager to get the artefact, the Kig-Yar again boarded the vessel via the umbilical.
The Unggoy Dadab was tasked with collecting the ship's signal unit, he made his way to an elevator and made his way to the command cabin. Halfway down the passage to the cabin, the Deacon suddenly remembered the disgusting filth that had awaited him in the other ship. As he stepped through the cabin door, he involuntarily held his breath and shut his eyes. Clang! Something heavy slammed into Dadab's tank. He yelped with alarm and staggered forward. Another blow knocked him to his stomach. Methane hissed from a fracture in his tank. Dadab shrieked for mercy, curling into a ball and covering his face with his spiny forearms. He heard a series of guttural exclamations, and felt something kick the back of one of his legs. Dadab parted his arms ever so slightly, and peeked through the crack. Here Dadab was, the first member of the Covenant to lay eyes upon a Human:
“The alien was tall and muscular. Most of its pale flesh was covered by a fitted cloth jumpsuit. Teeth bared, and holding a red metal cylinder above its mostly hairless head, the thing looked savage—not at all like something that might possess a holy relic.”
Unable to communicate with the creature, the Unggoy rolled up in a ball and covered his eyes. Instead of the killing blow that Dadab had expected, he heard the cylinder bounce off the rubbery floor, and roll to a stop against the side of the cabin. Uncrossing his arms to look at the alien, Dadab was surprised to find the human lying dead next to him. At first the body showed no signs of harm, but then the Unggoy looked at the back of the creature's head. In the defence of his Unggoy companion, the Huragok Lighter Than Some had thrown his weapon, a hunting rock, into the alien's skull, killing it instantly. After the Kig-Yar had searched the ship for the Forerunner relic, they did not discover one. Enraged by this, the Ship Mistress ordered the ship to be destroyed and the Transgression made their way further into the star system.
On the nearby planet of Harvest, the Human artificial intelligence Sif had simultaneously been keeping track of hundreds of in- and outbound ships. These ships would drop out of slipspace just outside the star system and she would lead them to Harvest on a set trajectory. Out of all these hundreds of ships, the This End Up stood out. As was a requirement for all ships approaching Harvest, they had to keep a set speed, in order to cross the distance to Harvest in a set time. But the This End Up went a little slower, less than 500 meters per minute, which would cause problems. Sif went to hail the ship, but there was no response. Then the freighter disappeared from her scan. Or more specifically, the single contact that was This End Up suddenly turned into many hundreds of millions of smaller contacts. Sif immediately contacted her human caretaker on Utgard, who was still awake, well past midnight.
Sif informed Jilan al-Cygni that another ship had disappeared, apparently blown up, from her sensors. Jilan looked over Sif's collected data and noted that there were 30 ships on that same trajectory, and was looking for something that would make the ship stand out. Jilan found it, the This End Up was the only ship with a captain. An actual human crew.
On Harvest, Staff Sergeant Avery Johnson was training new recruits for the Harvest Militia. It was Avery's job to train these farm boys to become adequate fighters against the Insurrection, but Avery struggled with the recruits. About half of them were members of Harvest’s law enforcement and other emergency services, so they were at least mentally prepared for the rigors of basic training. But these men were older as well (some in their late forties or early fifties), and they weren’t all in the best of shape. Avery had them for a few weeks now, and were on their first 10 kilometre run with 25 kilogram rucksacks along Gladsheim Highway.
Avery was later called in to Jilan's office to brief him on the events that had taken place several thousand kilometres from Harvest. Convinced it were in fact Insurrectionists that were responsible for the destroyed freighter. She ordered Avery to investigate the event, Avery, together with Staff Sergeant Nolan Byrne boarded the UNSC Walk of Shame to provide bait, armed with XBR55 Battle rifles. They did not have to wait long before the ship was caught on the Minor Transgression's sensors.
There would be no surprises this time. Chur'R-Yar had made sure of that. Through the walls of the umbilical, she could see the boxy freighter’s atmosphere venting out the careful holes she’d made with her own ship’s lasers. If any of the aliens were hiding on board, the Ship Mistress had done all she could to kill them without harming whatever relic lay inside. After the surprise encounter on the last freighter, Chur'R-Yar and the other Kig-Yar had scoured the alien ship. But they found no relics. Even Minor Transgression's Luminary had given up and dimmed its glyph. In her frustration, the Ship Mistress decided to destroy the vessel—obliterate all evidence of her fruitless transgression.
Together with the Kig-Yar Zealot Zhar, Chur'R-Yar entered the alien ship. The first thing Chur'R-Yar noticed inside the hold was the lack of gravity. Floating half her height above the floor, she realized her laser fire must have hit an essential part. Looking through the hold in search of the Forerunner relic, the Kig-Yar were suddenly under fire. Chur'R-Yar retreated as fast as was allowed in the micro-gravity, going straight back to her ship's bridge to disconnect the umbilical.
It was Nolan who had fired at the Kig-Yar, and he and Avery quickly followed them into the alien ship. After Nolan and Avery had dispatched of the Kig-Yar, Avery was able to send a report to Jilan on the ground:
"They aren't Innies. They're aliens. Kind of like lizards without the tails."
The Transgression then self-destructed, instigated by the Zealot Zhar. Only Avery, Nolan, Dadab and Lighter Than Some survived.
The Ship Mistress had disconnected the luminary from the ship's communication, which had since been reconnected by the Huragok engineer Lighter Than Some. This allowed the luminary to send all the information it had gathered of the Forerunner relics back to High Charity. This transmission was received by the Minister of Fortitude and the Vice Minister of Tranquility. To keep the Sangheili from using this discovery as a way to upset the balance of power, they utilize a Jiralhanae-controlled ship, Rapid Conversion, captained by Maccabeus, the Jiralhanae Chieftain at that time, and crewed by his pack of Jiralhanae. They began a secret attempt to seize the planet.
Rapid Conversion arrives in the system to find the escape pod containing Dadab and the Huragok, Lighter Than Some, much to the devout Maccabeus' delight. The Jiralhanae use the Deacon as a way to motivate their own lackluster complement of Unggoys and Lighter than Some. The Jiralhanae land two Spirit dropships at a specified date, with only the desire to capture the entire planet at any cost. The attempt at peaceful contact falls apart after an errant Unggoy attacks Harvest Colonial Militiaman Osmo, and the one-sided Battle of Harvest begins. During the battle Maccabeus is ordered to simply glass the planet from orbit, but the Chieftain disagrees. As the luminary showed them, there were many relics on the planet, and he did not want them destroyed.
This led his young nephew Tartarus to challenge his uncle for a fight for the Chieftainship, which Tartarus wins. The ruthless Tartarus then orders his new pack to assault the space elevators the humans are using to flee the planet. After destroying the space elevators, he starts to glass the planet. It will take months before Harvest is fully glassed, but in the meantime the Human-Covenant war has officially started. The Covenant Hierarchs repurpose the luminaries as a means to locate human planets.