Hoshi and Trip have to beam to Enterprise because of a storm. Hoshi is freaked out about using the transporter. This is an appropriate theme for Enterprise, but unfortunately it’s been well covered in Star Trek already.

Since Hoshi was almost in a storm Archer lets her take a nap instead of reporting for duty

Hoshi feels like people aren’t talking to her as much

Hoshi starts disappearing every now and then. The writers must have felt like it was poetic to combine her becoming invisible along with people ignoring her and acting like she’s invisible. It mostly just doesn’t make sense. Neither of these things would be caused by a transporter accident, and especially not at the same time. If she started to go semi-transparent, people would take notice

Hoshi can’t do simple translator stuff, and that idiot other guy did it way better than her. She’s not herself!

Then Hoshi becomes invisible to people.

Everyone thinks Hoshi is dead. Trip asks to be alone with what they think are the remains of Hoshi. He just gets mad at her for not listening to him

Some aliens are fiddling around with things on Enterprise. Only Hoshi knows about them. She has to warn everyone!

Hoshi can go through walls, but not the floor. She also can manipulate a little light that she uses to communicate with Archer. Basically her capabilities are whatever the plot requires

At some point the episode ends and everything is better