Last week, the final seven groups treated us to some Halloween medleys. But one group failed to turn a trick, leaving the Yellowjackets stung. Now six remain in the hunt for $200,000 and the Sony Music recording contract.

First up, consider this your "Wake Up" call from Arcade Fire.

Now... to battle. First up... (Olmec) LET'S ROCK. (/Olmec)

1) PENTATONIX blew out the competition last week, but they fear that they don't have the vocal power to carry a big rock anthem. And Kirstie being sick ... doesn't help. They'll give it all they have with "Born to Be Wild" by Steppenwolf.

That's the key to this competition. If something looks like it doesn't work, you make it work. This is Pentatonix at its element, from the bass-heavy arrangement to the natural blend to the animated choreo. The mark is set. Everything seems to work when it's supposed to.

2) DARTMOUTH AIRES are not going to take it anymore. Last week, they took on Queen, but they'll have to do better, but can they do it with one less bass, who is off to grad school? We're gonna see with Dee Snider's love letter to my generation, Twisted Sister's "We're Not Gonna Take It".

That... could've been tighter. Yes, rock'n'roll is about rebellion, but you have to remember, you are a unit. Even as interesting as the breakdown post-bridge was, you can be as loose as you want, but you have to cohere. Luckily you have one song left.

3) AFRO-BLUE are classic jazz stylists, but they need to embrace a less-is-more approach. And they need to do it with a Tom Petty classic, "American Girl". Can they turn rock blue or will they be left feeling blue?

They tried to put it at the speed of Afro-Blue, but there was a hole in the chorus that you could drive a Mack truck through. Nice interpolation of the National Anthem. But it's one of those cases where, are you doing it because you feel it, or are you doing it just to avoid elimination? Ben... calls you out. They need to find identity before they can find accessibility.

4) DELILAH ... they need help. They've been skirting by the seat of their pants for the last couple of weeks, and now they face a must-blow night. Will they get the performance that they're looking for on "Dream On" by Aerosmith, or is this going to be something that will cushion the blow of an all-but-certain death?

The good: the arrangement. The bad... the all-over-the-place choreography. The ugly... wind machines and power shrieks. You ladies better enjoy your last song, because I think, and this is just me talking, but I think... that your last song... is JUST THAT.

5) URBAN METHOD - They are innovators. They are favorites. But can they adapt to a musical genre that is not their own? We'll see the end result on Whitesnake's "Here I Go Again". They're trying to incorporate a rap into it. What they need to incorporate is confidence.

Afro-Blue, take notes. This is how you make a strange song work for you. They play the performance to their strength, and it sounds fresh and new. This is why Urban Method is in the place that they are in.

6) VOCAL POINT - They've had some up moments and some down moments. But their biggest challenge... school. Pretty much going on fumes at this point, but they can use that on their performance of "You Really Got Me" by the Kinks.

Started out safe, but with a few well-timed turnabouts, you salvage the performance. Interesting staging with the band mock-up. Combine that with a good blend and a nice arrangement, and you have a winning performance, but they need to continue on the high and not fall back.

Meanwhile, what's up with fellating the mic, sir?

We've gone rock, now it's time to go country.

1) DARTMOUTH AIRES - "Save A Horse, Ride A Cowboy" by Big & Rich

You have to be VERY tight in order to pull off a cappella while line dancing. They pull it off. And they keep it a little bit interesting with the arrangement, especially in the coda of the tune and the octave play throughout. It was a lot of fun to watch. And it should be.

2) AFRO-BLUE - "Need You Now" by Lady Antebellum

It's not that big a stretch from jazz to country. And like the last performance, it's not one big thing, it's several small things, like breath control and a sharp note here and there. Otherwise, it's perfectly passable. Of course it helps that the song crossed over into the pop chart where you can pretty much turn it into anything.

3) URBAN METHOD - "Before He Cheats" by Carrie Underwood

I think the ladies found their confidence.

4) DELILAH - "If I Die Young" by the Band Perry

Sung like a group that is resigned to their fiery fate. There was minimal blend and no dynamic whatsoever. It was just ONE LOUD PHRASE AFTER ANOTHER!

5) VOCAL POINT - "Life Is A Highway" by Rascal Flatts

Again with the stage theatrics. Good arrangement, and a great grasp of what the song is about. It's about life... as a highway. That's freedom, baby.

6) PENTATONIX - "Stuck Like Glue" by Sugarland

If you remember, Kirstie is singing wounded. She inflects like a pro, though. And the group follows her every move. No doubt the best of the night. And how about the reggae switch-up in the middle? That is money in the bank.

We've had rock. We've had country. Now someone's about to sing their way back to the house.

Returning next week.... Pentatonix and Urban Method!

Joining them... Vocal Point and Dartmouth Aires!

That leaves Afro-Blue and Delilah in the bottom. Afro-Blue has trouble connecting to the music. Delilah was pitchy and weak on their second performance...

Leaving tonight ... DELILAH. They sing us out with their swan song, "Survivor" by Destiny's Child.

The a cappella geek has spoken...

Power Rankings after Week Eight:
PENTATONIX
URBAN METHOD
DARTMOUTH AIRES
VOCAL POINT
AFRO-BLUE

We're down to the final five. Next week, we're getting our soul on. Who'll bare their soul for another week in the competition, and who'll sell out their soul for the next ride out? Until next week, this be Achordant #5 reminding you to support local and independent music!

To see this episode in its entirety, visit www.nbc.com/singoff.