Hadley's Hope was a human colony that was established by Weyland-Yutani sometime in the twenty-second century on Acheron LV-426 and which in 2179 maintained a constant population of 158 colonists. It was named after the colony's leader, Curtis Hadley.
Weyland-Yutani gave orders to the colonists to investigate the ruins of the Derelict spacecraft where they discovered thousands of Xenomorph eggs in suspended animation. Soon the eggs began to hatch and the Facehuggers started to impregnate the colonists. The colony was eventually overrun by the Xenomorphs, leaving only a lone colonist alive by the time the United States Colonial Marines arrived.
After the mysterious loss of contact with the colony, Weyland-Yutani corporate employee Carter Burke recommended to the company that they send himself along with Ellen Ripley and a team of USMC soldiers to investigate. It didn't take long for Weyland-Yutani to green-light the operation, and shortly thereafter the USS Sulaco was dispatched with all of the above on board. When the expedition landed on Hadley's Hope, they discovered obvious signs of a relatively large, violent struggle, as both the complex's exterior walls and its interior hallways were riddled with marks from recent small arms fire, and some of the areas had suffered more extensive damage, consistent with the use of explosives.
The marines' initial investigation of the seemingly abandoned colony was being broadcast (via their helmet cameras) back to the Sulaco. Ripley, viewing the investigation over the monitors back on the ship, noticed a rather peculiar looking hole in the floor on Corporal Hicks' feed as he proceeded down a hallway. Terrified, Ripley made the announcement that the hole could've only been made by molecular acid, suggesting that one of the colonists, not knowing about their acidic blood, had shot at and wounded a Xenomorph. Ripley, along with Carter Burke and Corporal Hicks' Squad, entered the compound shortly thereafter, at which point they came upon a barricaded section of the hallway where it appeared that the colonists, in their desperation, had made their last stand. After further investigation it was confirmed: the colonists had blocked off both ends of the hallway with large, heavy equipment before welding it all together at the seams in an effort to keep the Xenomorph horde at bay. Ripley theorized that, unfortunately, the colonists efforts had been in vein -- the barricades hadn't held, and their desperate last stand wasn't enough to stop the aliens from exterminating the majority of them, while Facehuggers claimed the rest as reproductive vessels to be taken to the hive during gestation. Shortly thereafter, the team stumbled upon a cocooned -- but barely alive -- colonist, who immediately woke up upon their arrival and began expressing equal parts panic and relief at the team's arrival, believing that they'd come to save her. Before anyone could do anything to help her however, they watched her die as a Chestburster xenomorph violently pushed its way through her sternum, evoking in Ripley the memory of the terror she'd felt in the galley of the Nostromo as she watched Cain suffer the same gruesome fate.
A short time later, the group stumbled upon a child, the colony's sole-remaining survivor: Rebecca Jorden. Rebecca (or "Newt," the nickname the team lovingly gave her) had survived by hiding in the complex's ventilation system where, miraculously, she was never discovered by the xenomorphs. Unbeknownst to the team, it wouldn't be long before Newt (and by extension, her newfound protectors) would come face-to-face with the alien creatures she'd managed to stay hidden from ever since they'd massacred every other colonist on the planet. The investigation had only continued for a short time after Newt's discovery when the team was ambushed by several xenomorph drones and suffered massive casualties, as they'd been completely unprepared for the aliens' propensity to take their prey by surprise.
After this skirmish, the handful of surviving marines, Ripley, and Newt, decided to evacuate the planet with the aim of nuking the colony from orbit. However, when they called the drop ship back to the planet's surface so they could board and subsequently execute their plan, an alien stowaway (who had secretly entered the ship while Ripley and several other members of the team were watching the marines initial investigation on the ship's monitors) killed the pilots, causing the ship to crash into the processing station, totally destroying the ship and critically damaging the station. It was then that Bishop, the team's android, informed the group that owing to the damage, the processing station's power plant had become extremely unstable, and would shortly explode with the force of a thermonuclear weapon. After apprising the group of that situation, Bishop then volunteered to pilot the Sulaco's remaining drop ship to the surface by remote control so that the group could escape the planet with their lives. This would take time, however, so the group went about beginning their preparations for the journey home.
Meanwhile, Carter Burke, whom had separated from the group discretely after receiving orders from Weyland-Yutani, secretly released two facehuggers from their tanks to achieve two ends: First, Weyland-Yutani had ordered him to cover up the company's involvement in the massacre at Hadley's Hope by any means necessary, and second, he'd hoped that the facehuggers would impregnate two of the survivors, whom he could then use to smuggle two living alien specimens through the quarantine back on Earth (as the authorities posted at the quarantine would have no idea that the survivors Burke was bringing through were actually host to two chestburster aliens within their bodies) so that he could then return the specimens to Weyland-Yutani in the hopes that he'd be rewarded, ascending the corporate ladder at the company.
While waiting for Bishop to finish preparations to fly the dropship to the surface, Ripley and Newt entered the medical laboratory where, despite intending to treat some wounds, instead succumbed to their exhaustion and fell asleep. Shortly thereafter, however, Ripley awoke with a start to the sound of several tiny fingers as they skittered quickly across the cold linoleum floor. Realizing that there must be facehuggers on board, Ripley immediately screams to alert the remaining marines to their situation, and manages to keep the spider-like creatures away from herself and Newt long enough for the marines to arrive and destroy the aliens, saving their lives. Ripley then accuses Burke of trying to impregnate her and Newt and get two alien creatures past Earth's quarantine and planning on killing the rest of the marines in hypersleep during the return trip back to Earth. Although the Marines are enraged by this and wish to kill Burke, Corporal Hicks intervenes, saying that the Xenomorph onslaught is a more pressing issue than resorting to vigilantism. Hicks proposes that Burke be evacuated from Hadley's Hope along with the rest, where he will stand trial on Earth, and warns "there is no way you are weaseling out of this one".
The Xenomorphs then cut the electricity and attack and kill the rest of the team and capture Newt and take her back to the hive. Ripley, Hicks and Bishop remain. Ripley and Hicks, who was injured during the attack, reach Bishop and the second drop ship, but Ripley is unwilling to leave Newt behind and make her another victim of the alien threat and reproduction. So she as well as Bishop and Hicks take the second drop ship to the processing station where Ripley rescues Newt. They then encounter the alien queen and her egg chamber that Ripley mostly destroys, enraging the queen, who escapes by tearing free from her ovipositor. Closely pursued by the queen, Ripley and Newt rendezvous with Bishop and Hicks on the drop ship and escape moments before the colony is consumed by the nuclear blast.