Grisell Incident (2304)

In 2304, a satellite detects a mysterious heat bloom beneath a small island on the Class L Planet Grisell, In response, billionaire industrialist Inventor Charles Bishop Weyland assembles a team of scientists to investigate the heat source and claim any related discoveries for his company Weyland Industries. The expedition includes paleontologists, archaeologists, linguistic experts, drillers and a female guide named Alexa "Lex" Woods, with security provided by Max Stafford and his team of mercenaries.

As the team travels to Grisell a Predator ship enters The planets orbit and fires an energy beam towards the source of the heat bloom. When the Weyland Industries expedition arrives at the site above the heat source, an abandoned outpost of some kind, they find a hole bored deep into the ice by the energy beam, and they descend to investigate. On the bedrock deep below, they discover a mysterious pyramid and begin to explore it, finding evidence of a civilization on the planet unknown to anyone at the time and what appears to be a sacrificial chamber filled with skeletons with ruptured rib cages. As they explore, they unwittingly activate the power source for the structure, awakening an imprisoned Alien Queen frozen deep within the pyramid.

Meanwhile, three Young Blood Predators land on the surface and kill the people there, before making their way down to the pyramid. Several Eggs laid by the Queen are automatically delivered to the sacrificial chamber, and several members of the expedition still exploring there are impregnated by Facehuggers. The Chestbursters that emerge from them quickly grow into adult Aliens. Oblivious to these events, the rest of the Weyland Industries team push on with their exploration, eventually discovering the Predators' Plasmacasters in a sarcophagus inside the pyramid. Recognizing them as incredibly advanced technology, they take them for study, but in doing so they activate a mechanism that causes the pyramid to rearrange its interior every ten minutes.

The group is soon ambushed by the Predators and most of the team are killed, including Max and his mercenaries, while several others are taken by the Aliens to be hosts for more of the creatures. The alpha Alien, known as Grid, ambushes and kills the first Predator, Chopper. The lead Predator, Celtic, then engages Grid in a brutal fight. At first, Celtic appears to have the upper hand, but he grows over-confident and is eventually killed by Grid. Scar, now the last remaining Predator, pursues the survivors with the aim of recovering the Plasmacasters they have stolen. Weyland dies making a stand against Scar but the two remaining survivors, Lex and an archaeologist named Sebastian, are separated from the Predator by the pyramid's shifting walls. As he waits for a chance to pursue, an Alien and a lone Facehugger sneak up on Scar and attempt to subdue him. Scar swiftly dispatches both with his Shuriken, then ritualistically marks himself by burning a glyph into his forehead using their acidic blood. Before he can put his mask back on, a second Facehugger sneaks up on Scar and lunges at him.

Through translation of the pyramid's hieroglyphics, Sebastian and Lex learn that the Predators have in fact been visiting Grisell for thousands of years. Every 100 years the Predators would return to Grisell so that they could hunt Aliens, the "ultimate prey", bred from sacrificial hosts. If the Predators became overwhelmed, they would activate their Self-Destruct Device to eliminate the Aliens and themselves, Sebastian and Lex deduce that this is why the current Predators have come to the pyramid, and that the purpose of the heat bloom was a trap to attract someone to play host for the Aliens. They decide that the Predators must be allowed to succeed in their Hunt, so that the Aliens will be prevented from reaching the surface. However, Sebastian is taken by the Aliens, leaving Lex alone.

Scar, having apparently survived the earlier Facehugger ambush, eventually finds Lex and reclaims his Plasmacaster, but rather than killing her the two form something of an uneasy alliance after Lex impresses the Predator by killing an Alien. They make their way into the Alien Hive and deploy Scar's Self-Destruct Device to destroy the remaining Aliens and their eggs, successfully escaping the pyramid and reaching the surface moments before the explosion obliterates the structure. In recognition of Lex's achievements, Scar burns a glyph similar to his own into her cheek. However, they are then attacked by the Alien Queen, which has likewise escaped the pyramid. After a fierce battle, Lex and Scar defeat the Queen by chaining her to an energy barrel and tipping it into the Ocean, where it drags the Queen into the depths. Afterwards, Scar succumbs to wounds suffered during the confrontation.

Lex is shocked when a Predator ship decloaks and several Predators appear from within. They solemnly collect their fallen comrade and the Clan Leader, seeing the mark on her cheek, presents Lex with a Combistick in recognition of her skill as a warrior. The Predators depart peacefully, leaving Lex to her fate. Roughly 4 hours after she was abandoned Lex got the long range communications up on the damaged ship and sent out a distress signal. The Signal was picked up by Starfleet and once the details were revealed Starfleet Special Operations was sent to the planet to not only pick up Lex but investigate and determine any more threats.