Development of the next Half-Life game

Half-Life 2: Episode Three will be the third and last installment of the Half-Life 2 episodes trilogy story arc, after Half-Life 2: Episode One and Half-Life 2: Episode Two.

Development
Like other Half-Life 2 episodes, Episode Three will follow the adventures of Gordon Freeman and likely Alyx Vance. Parts of the episode will probably be set farther north, possibly in arctic conditions. Valve has said that they intend for each episode to highlight a major new feature or gameplay design element. In Episode One, this was the interaction with a well developed NPC, along with full implementation of the Source's High dynamic range rendering ("HDR") lighting system. In Episode Two, this was creating large outdoor environments, battles previously unseen in the Source engine, performance and rendering enhancements to the Source engine to accommodate multi-core processor architecture and a new cinematic physics system to create large physics-based events. The new gameplay and Source engine features for Episode Three are currently unknown. It has been stated that Episode Three will be the final episode of the Half-Life 2 universe story arc, but not the end of the Half-Life franchise. What happens next for the franchise is currently unknown.

Valve marketing director Doug Lombardi has stated that news on or an announcement of Episode Three may be revealed near the end of 2008. But it didin't.

Plot speculation
The plot of Episode Three is largely unknown. What follows is speculation deduced from the events of Episode Two.

Judging from events at the end of Episode Two, it will involve Gordon Freeman and Alyx Vance moving even further away from City 17 to an arctic setting. The plot is expected to revolve around the Borealis - an ice-breaker vessel belonging to a former rival of Black Mesa, Aperture Science. It is implied that some powerful technology exists on board and the main objective of Episode Three will probably be to find the ship and the technology on board whilst rescuing Dr. Judith Mossman in the process. The action to be taken is unclear since Isaac Kleiner and Eli Vance showed their disagreement about whether the technology on board should be destroyed to prevent another catastrophe or retrieved for use against the Combine. Eli was killed at the end of Half-Life 2: Episode Two, so it is unclear about who will be leading the resistance. The decision about the use of this unknown technology now rests only on Kleiner's decision. Eli's death may change his mind and in either case, Alyx may wish to honor her father's last direction to destroy it. Episode Three being the final episode, it is also possible that there may be a function of player choice towards the end that affects the outcome; however, like Half-Life's ending, only one of the choices will end up as canon.

Characters
It is anticipated that the player will see a glimpse of the G-Man's overarching plan for Gordon Freeman and Alyx Vance, as well as the "unforeseen consequences" and the role of the Vortigaunts, who seem to have taken more control over the situation.

The fate of several characters in the game may also be revealed. It is not known whether Judith Mossman is still alive after being tracked down by Combine forces and as she was the subject of Gordon and Alyx's journey northward it is presumed her fate will be revealed. Barney Calhoun's absence from Episode Two may also be explained, though it is unknown whether he will reappear in the third episode. The overall status of Dr. Breen is also ambiguous, as though his appearances are minor in Episode One and Two (especially a brief moment in the latter), they are still significantly present and his fate is ultimately unclear.

Enemies
According to the concept art, Advisors are known to be encountered, though most details are unknown until more information is released. However, it can be reasonably assumed that most of the existing Combine units like the Combine Soldiers and Hunters will be encountered, especially since they were seen in Mossman's video.

Also, not a single Half-Life game yet has lacked Headcrabs, Zombies, or Barnacles, so they are likely to make appearances.

The technology inside the Borealis
The technology located inside the Borealis is possibly a form of teleportation technology, although this is unlikely because the Citadel contains a trans-dimensional teleporter which allows the Combine to travel between their universe and Earth, and both the Combine and the resistance possess localized teleportation rendering portals impractical. If the pattern continues to repeat, the Aperture Science technology will likely be a highly efficient and accurate form of portal like the Portal Gun, but capable of moving much larger objects than an individual person, such as a whole ship (and part of its drydock).