Mission Improbable is a singleplayer mod for Half-Life 2: Episode 2. In it, Gordon Freeman is tasked with re-activating a Resistance listening post. From there, things quickly escalate.
There is much to explore and discover in this mod. A very Half-Life-2-centric mod with plenty of combat and storytelling. Beautiful vistas throughout, epic brushwork, and plenty of custom content. Especially impressive final chapter.