When a military-trained biologist’s husband unexpectedly returns alive from a secret mission, she must go on a quest to a mysterious lighthouse to save his life – and the world.

The military-trained biologist sounds like that weird Natalie Portman movie.

Like others I wonder what is in the lighthouse? Aliens? Some other creatures? A disease?

I was thinking similar to above comment -

A biologist's husband, the sole survivor of a military mission, returns afflicted with X. She retraces his steps to a mysterious lighthouse to save his life ? and the world.

I just don't see the logical, causal connection between his return and her need to go to the lighthouse, how the former triggers the need to do the latter.

However, what if she's told he's MIA -- missing in action --- on a secret mission, then her objective goal is to find him, or find out what happened to him.? She has more personal and urgent stakes in going on a quest... that leads to the lighthouse.

fwiw