Apparently, this episode has no theme other than "Dance real good." After the couples come out, Tom points out that Tamar is absent. She was taken to the hospital during dress rehearsal and it's unclear if she'll be back at the studio in time and able to perform.
The opening sequence featuring clips of the semifinalists is trying to be all tense and dramatic and uber-competitive. Then the show starts and the troupe and pros are doing a goofy jive with a bowling theme. Tonal whiplash.
The opening credits tell us that 10 years ago a tradition began, and we see brief clips of some of the past winners. Then we're told tonight a new dance era begins, before this year's "stars" are introduced. This year more than ever it's hard to defend the show's definition of "star." I have no idea who half these people are.