The Sarah Jane Adventures/Recap/S4/E07 E8 The Empty Planet

Clyde and Rani awaken one morning, to discover that everyone on Earth has mysteriously vanished, even Sarah Jane and Mr. Smith. Whilst exploring the deserted London, they encounter a boy named Gavin, who's just as confused as they are. Eventually, the force behind the disappearance of the human race make themselves known, a pair of cyclopic robots, one red and one yellow, began to chase the three teens through the deserted streets.

Tropes

 * Adam and Eve Plot: Clyde attempts to invoke this trope. Rani isn't so keen.
 * Continuity Nod:
 * Cyber Cyclops: Both of the robots.
 * Interspecies Romance:
 * Half Human Hybrids:
 * The Last Man Heard a Knock: The only three people left on Earth all run into each other. Rani literally finds out she's not alone by Clyde knocking on her door.
 * Secret Legacy:
 * Ship Tease / Will They or Won't They: Clyde and Rani.