Big Brother determined the week's four nominations only to subsequently dethrone one of the two Head of Households, leaving two houseguests on the chopping block during Sunday night's 21st broadcast of the show's sixteenth season on CBS.

Big Brother's 21st episode began following the aftermath of the double eviction in which both Jocasta Odom and Hayden Voss got eliminated from the competition.

Nicole Franzel, who had also been on the block alongside Hayden, was shocked about the turn of events and all the betrayals. She knew Christine Brecht, her former best friend in the house, had been conspiring against her. Likewise, she thought Frankie Grande was working with her when he apparently wasn't.

Despite Derrick Levasseur's attempt to claim Victoria Rafaeli had been responsible for flipping the house, Nicole still had a meltdown and blew up Christine and Frankie's spots. Nicole revealed Frankie and Christine had been in an alliance with her and Hayden, ultimately hoping to target and evict Zach Rance -- whom Frankie had a "Zankie" bromance with.

Frankie denied the accusations, only infuriating Nicole further, but no one really believed Frankie because he wasn't prepared to make convincing arguments. Derrick avoided all the heat although it was pretty much his fault -- in addition to his closest "Hitmen" ally Cody Calafiore -- that lines were drawn in the sand, separating Nicole, Victoria and Donny Thompson from the "Detonators" alliance.

The "Detonators" alliance was comprised of Zach, Frankie, Derrick, Cody, and Christine. Caleb Reynolds believed himself to be a part of that alliance, presuming it was still called "The Bomb Squad," which had previously also included Amber Borzotra. However, Caleb was just a pawn to the group of allies.

It then became time for the Head of Household competition, and Caleb was deemed ineligible to compete because he was the outgoing HoH.

The HoH competition took on the format of a tournament-style trivia game. After rounds of different brackets, Nicole and Christine ended up both being crowned Head of Households. Nicole was weirded out about the thought of scheming with Christine since she had lost all trust in her friend, however, Derrick was happy about the competition's results because one of the "Detonators" was in power.

In a desperate attempt to get back on Nicole's good graces, Frankie devised a plan to reveal he had been working with the other side of the house in an all-male alliance but those guys had turned against him. He declined to disclose Christine was also a part of it.

Frankie then suggested to Nicole and Christine they should work with the odd ones out in the house -- Donny and Victoria -- to flip on the boys and therefore nominate Caleb, Cody, Derrick, and Zach.

Christine disliked the idea because Frankie never talked to her about what she wanted. She also had loyalties with some of the guys and really trusted them.

Zach then tried to mend things with Nicole to avoid getting nominated again. He expressed anger over Christine and Frankie's lies and begged Nicole to work with him. Nicole wasn't certain that Zach was capable of keeping his mouth shut, so in a last-ditch effort to put his game in Nicole's hands, Zach blew up the "Detonators" alliance and totally came clean.

A shocked Nicole admitted that she was supposed to be in an alliance with Cody and then revealed to Zach how Frankie had just suggested nominating four of the guys. Nicole knew Zach would run back to his alliance and share the news with him, and that he did. Zach told Caleb about Frankie's idea, and then Caleb turned around and told Derrick and Cody.

Derrick determined Frankie needed to go as a result, so he insisted that Nicole should nominate Frankie and someone who would be willing to throw the "Battle of the Block" competition in order to keep Frankie on the chopping block. Nicole trusted Derrick because she felt he had never lied to her, and then she approached Caleb to tell him that Frankie had put her up to lying about Amber during the week of Amber's eviction.

Caleb was furious and therefore volunteered to go up on the block next to Frankie.

At the nomination ceremony, Christine announced she had decided to nominate Donny and Zach because she was intimidated by Donny's intelligence and Zach was just an obvious choice because he had previously nominated her.

Nicole then opted to nominate Caleb and Frankie, admitting that she wanted Frankie gone because he had thrown so many people under the bus. Christine was blindsided but respected Nicole's big move. Zach then announced Christine and Frankie were dead to him in the game. Despite Frankie's efforts to talk and work things out, Zach ignored him.

It then became time for the NFL-themed "Battle of the Block" competition in which Frankie and Caleb were set up to battle Zach and Donny.

Frankie had a feeling Caleb was going to throw the competition and pleaded with him not to. However, Caleb didn't just throw the competition -- he actually chose to sit it out entirely and simply watch Frankie struggle. Caleb was honest about the fact he was avenging Amber and pissed at Frankie for turning on the guys.

Although Donny and Zach got off to a strong lead, Frankie pulled ahead and ended up winning the competition all by himself. Caleb and Derrick's plan completely backfired, and Zach and Donny remained on the chopping block.

A teary-eyed Frankie said he played in the competition for his deceased grandpa, Ariana and the entire Grande family. None of the houseguests seemed to notice his older-sister reference.

Frankie then determined he might be able to win back the trust of his fellow houseguests by revealing the fact Ariana Grande, a famous singer, is his sister. He thought the news might work to his advantage.