They're exploring a new area and find some crystals. Red crystal + yellow crystal = boom. Blue + Green = no reaction. Red + blue = no reaction. Yellow + red + blue = terribly shocking experience.
All his strength has been drained.
Holly gets her father back to the cave, while Will outruns Big Alice to get into the lost city and seek help from Enik.
Since she can't haul the basket up by herself, she's set up a counterweight basket and is putting things in it so the basket with her father in it will be hauled up.
She manages to get him inside the cave.
Will tells Enik they need his help, but Enik's too busy working with the dimensional doorway. (Which is a problem in the series. Didn't he go through a doorway once already? There hasn't been anything in the episodes which explains why he's still there.)
The dimension doorway works just like the time portal in City on the Edge of Forever.
Enik has an ego problem. Since Will did not return to Earth when the doorway showed it, his sacrifice would be greater than Enik's, and that's something Enik he says he can't allow.
Enik helps cure Rick.
Note this picture. Enik has left, but someone has forgotten the special effects, so you can see Enik's shadow on the blue screen put up outside the “cave” entrance.