Watch My Stepmother Is an Alien

Celeste is an alien envoy headed to Earth while Steven Mills is a widowed scientist working on new ways of sending radio into deep space. After an accident causes the disruption of gravity on Celeste's planet, she investigates who is responsible and how such an attack is possible. Her arrival on the planet Earth involves crashing a party held by Steven's brother Ron. Her initial appearance is mocked, thanks to the 20 year delay in receiving broadcast transmission, due to looking like someone from twenty years earlier.

Celeste's lack of experience almost causes her to expose her alien nature, such as trying to kiss or cook. Jessie, Steven's tween daughter notices Celeste's odd ways but is unable to convince her lovestruck father of the oddity. Ron also has doubts, but his reasons lie more in Steven asking for Celeste's hand in marriage after only knowing each other for a few days. Ron's course of action involves mentioning that Celeste might be an illegal immigrant or a spy, though he also admits the envy he has with his brother meeting his dream woman.

Celeste's time on earth allows her to discover such things as sneezing and love making. When Jessie directly addresses Celeste about her otherworldly nature, Celeste reveals that her home world lacks any concept of emotion and that she will leave once she learns the truth. Jessie counters Celeste's plan by stating that such activity will emotionally ruin her father. Jessie later gets into an argument with her dad, running away and nearly hit by a car if not for the interference of Celeste, an act that reveals her alien nature to Steven. Celeste admits she loves Steven and accepts Jessie as a daughter.

Some time later, the leaders of Celeste's planet report in, with Celeste and Steven successfully convincing them that the antigravity was a scientific error. The leaders give their blessing to Celeste's intergalactic union but ask for an Earth native to become an ambassador. Ron accepts the ambassadorship and heads to Celeste's planet within a spaceship.