Cmdr. John Koenig has been replaced/taken over and the crew try to figure out what is going on. Maya, the resident shape-shifting alien, changes into another member of the crew to gain access to a mysterious crystal.
This was the mid-late 70's and budgetary restrictions as well as the lack of technology means there is no attempt to show the transformation.
However, most of the time Maya transformed into huge (rubber suited) space monsters so it makes a nice change to have her become another female.
