The Men in Black have always protected the Earth from the scum of the universe. In this new adventure, they tackle their biggest, most global threat to date: a mole in the Men in Black organization.

Agents J and K are back...in time. J has seen some inexplicable things in his 15 years with the Men in Black, but nothing, not even aliens, perplexes him as much as his wry, reticent partner. But when K's life and the fate of the planet are put at stake, Agent J will have to travel back in time to put things right. J discovers that there are secrets to the universe that K never told him - secrets that will reveal themselves as he teams up with the young Agent K to save his partner, the agency, and the future of humankind.

Kay and Jay reunite to provide our best, last and only line of defense against a sinister seductress who levels the toughest challenge yet to the MIB's untarnished mission statement – protecting Earth from the scum of the universe. It's been four years since the alien-seeking agents averted an intergalactic disaster of epic proportions. Now it's a race against the clock as Jay must convince Kay – who not only has absolutely no memory of his time spent with the MIB, but is also the only living person left with the expertise to save the galaxy – to reunite with the MIB before the earth submits to ultimate destruction.

Sabrina travels to Australia's Great Barrier Reef with her best friend Gwen, a fellow witch from England, for a week-long vacation where they try to help protect a hidden mermaid colony whose habitat is threatened by ocean pollution, and by a local marine biologist determined to find the colony as his claim to fame. While Sabrina finds romance with a "merman" from the mermaid colony, Salem the cat finds a possible romance with another witch-turned-into-a-cat, named Hilary, but finds Sabrina's problems interfering with his plans.

After a police chase with an otherworldly being, a New York City cop is recruited as an agent in a top-secret organization established to monitor and police alien activity on Earth: the Men in Black. Agent Kay and new recruit Agent Jay find themselves in the middle of a deadly plot by an intergalactic terrorist who has arrived on Earth to assassinate two ambassadors from opposing galaxies.