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.
The level design is utterly superb, and reminds me of something like Minerva: Metastasis. I also applaud you for getting Stephen Hawking, the brightest mind of this and the last century, to make a cameo appearance. Are you thinking of making a sequel?