I knew Tenaya would...
Be captured and (possible spoilers) reprogrammed.
It was so predictable, like with Astronoma going good and then being all controlled/reprogramed by evil.
According to tv.com:
Dillon's search for Tenaya is put on hold when Scott is in trouble. Scott was shot with a key that allows Shifter to control him. The rangers do their best to save their leader when they come face to face with Tenaya 15. She has been reprogrammed with one mission; Serve Venjix.
That's the next episode.