Bill's latest discovery is put in jeopardy, even as trouble brews with the human aliens; Catherine must decide where her loyalties lie.

With Adina's plan for world destruction reaching completion, and our heroes in the alternate world under attack, both sides must make great sacrifices if they are to save humanity.

With Adina's plan in motion, the world's last hope is for Bill to make one more journey, risking his own life in search of Catherine's help.

M.O.D.O.K., finding himself stifled by GRUMBL’s bureaucratic control of AIM, teams up with Monica to take down their new bosses. Monica's hatred toward M.O.D.O.K. remains, however, and she ends up betraying M.O.D.O.K., causing the two to have a mad scientist duel, which M.O.D.O.K. loses in front of his whole company. Monica is promoted to Scientist Supreme and M.O.D.O.K. is stripped of his authority. Meanwhile, Jodie's life without M.O.D.O.K. flourishes as one of her videos goes viral, launching her into internet fame.

One year after escaping the destruction of their planet Shlorp and crashing on Earth, aliens Korvo, Terry, and their child-replicants Yumyulack and Jesse adjust to their new lives. Korvo is determined to repair their spaceship, but Terry introduces him to the television show Funbucket. Realizing that the titular alien is fictional, they create a real Funbucket, who tires of them and befriends humans Travis and Avery. Forced to attend high school, Yumyulack and Jesse are menaced by their classmates and faculty. They shrink a bully named Lydia, hoping to use her to study human behavior. As the Shlorpian family have dinner together, it is revealed that their pet, the Pupa, will one day evolve and destroy Earth to terraform a new Shlorp.

Korvo and Terry place nanobots in the city's water supply to spy on their neighbors. Learning they are not well-liked, Korvo and Terry use the information from the nanobots to win over the community, and run for president of their homeowner association. The nanobots form a sentient person that runs for president as well, and all three expose embarrassing secrets about their neighbors, who break out in violence. The incumbent president Ruth restores order and turns the crowd against Korvo, Terry, and the nanobot person, who escapes from Korvo. Jesse – concerned that Yumyulack is shrinking and capturing too many humans – uses technology to manipulate people who were mean to Yumyulack, hoping to teach him that humans are generally kind.

With Adina's plan for world destruction reaching completion, and our heroes in the alternate world under attack, both sides must make great sacrifices if they are to save humanity.

With Adina's plan in motion, the world's last hope is for Bill to make one more journey, risking his own life in search of Catherine's help.

The BAU is called to Taos, N.M. to investigate an UnSub who is targeting his victims' temporal lobes.

When a web celebrity is murdered, Castle and Beckett explore the flashy world of internet fame, but when the killer posts pictures from the crime scene on a photo-sharing site, they realise they are up against a social media sociopath who may strike again.

When Reid discovers former FBI Special Agent Owen Quinn locked inside a storage unit, the BAU questions the credibility of Quinn's bizarre accounts of searching for an UnSub that he named "The Strangler".

Beckett and Castle investigate the shooting of an ice cream vendor and clues lead them to suspect that an unknown second grade child might be able to help them solve the case; Castle goes undercover at a school to try and find the student.

A new lead in Colter’s white whale case, the disappearance of Gina Picket, brings him and retired cop Keaton (guest star Brent Sexton) back together to track down a serial killer.

Athena and Bobby set off on their honeymoon cruise, but when duty calls, their vacation is put on hold; a fighter jet traps a civilian; an unusual incident leaves a couple stuck together.

A 15-year-old Jane Doe, who is hearing impaired and unable to communicate, is found on the streets covered in blood and wielding a knife, leading the team to believe she is responsible for a recent murder.

The BAU is called to Taos, N.M. to investigate an UnSub who is targeting his victims' temporal lobes.

When Reid discovers former FBI Special Agent Owen Quinn locked inside a storage unit, the BAU questions the credibility of Quinn's bizarre accounts of searching for an UnSub that he named "The Strangler".

When the GBI discovers that a neo-Nazi organization is planning an attack, they prioritize the case to protect innocent people; Angie faces a potentially life-changing scenario and investigates a sneaker release gone wrong with Ormewood.

A new lead in Colter’s white whale case, the disappearance of Gina Picket, brings him and retired cop Keaton (guest star Brent Sexton) back together to track down a serial killer.

The disastrous cruise continues when Bobby and Athena respond to the ship's explosion, racing to aid injured passengers; Hen questions her instincts in a life-taking call and grows concerned about Athena and Bobby's whereabouts.

When Castle gets knocked out while tracking some criminals with Becket, he wakes up to a world in which he and Kate have never met.

When sniper-on-the-loose Jacob Broadsky claims another victim, Booth becomes more determined than ever to catch his elusive foe.

When Castle and Beckett learn that a murder victim may have been poisoned at an Old West-style resort, they visit the resort posing as newlyweds to uncover the truth.

The BAU is called to Texas to search for an escaped killer known as "The Silencer", while the team welcomes its newest member into the fold.

When the bodies of two seemingly unrelated victims are found just hours apart in San Diego and Los Angeles respectively, the BAU suspects that that not one, but two killers are working together to commit these murders.

When a case that hits close to home comes across Will's desk, he discovers there is more to the incident than meets the eye; Angie and Ormewood investigate a murdered magician while uncovering some extra tricks that had been up his sleeve.

Beckett and Castle investigate the shooting of an ice cream vendor and clues lead them to suspect that an unknown second grade child might be able to help them solve the case; Castle goes undercover at a school to try and find the student.

When Castle and Beckett learn that a murder victim may have been poisoned at an Old West-style resort, they visit the resort posing as newlyweds to uncover the truth.

When Castle gets knocked out while tracking some criminals with Becket, he wakes up to a world in which he and Kate have never met.

When a case that hits close to home comes across Will's desk, he discovers there is more to the incident than meets the eye; Angie and Ormewood investigate a murdered magician while uncovering some extra tricks that had been up his sleeve.

When sniper-on-the-loose Jacob Broadsky claims another victim, Booth becomes more determined than ever to catch his elusive foe.

The BAU is called to Texas to search for an escaped killer known as "The Silencer", while the team welcomes its newest member into the fold.

The team identifies the remains of a successful ad man found in the grounds of a newly built community center playground.

A 15-year-old Jane Doe, who is hearing impaired and unable to communicate, is found on the streets covered in blood and wielding a knife, leading the team to believe she is responsible for a recent murder.

When sniper-on-the-loose Jacob Broadsky claims another victim, Booth becomes more determined than ever to catch his elusive foe.