Three new Organisation agents are pulled from their ordinary lives and sent to Philadelphia to investigate Operation Iapetus. A brutal family murder appears to be linked to a set of impossible hypergeometric numbers, and with the help of an unlikely conspiracy blogger, the team establishes a base of operations as they begin uncovering a mystery that was never meant to be understood.

The investigation into Michael Wei reveals an exceptional Columbia University student whose recent obsession with the forgotten mathematician Faustus Claudan may hold the key to the case. With no apparent link to the murdered Ridgeway family, the trail grows colder as Stevens and Smith race to secure an increasingly chaotic crime scene, where the greatest threat may be the hypergeometric sequence itself falling into the wrong hands.

While Smith and Stevens work to contain the fallout in Alliance, newly recovered doorbell footage captures Michael Wei's final moments and raises troubling new questions. At the same time, Dellaroche and Anderson search Wei's dormitory, uncovering the obsessive mind behind the killings - and the horrifying discovery that the hypergeometric sequence had already been disseminated before his death.

With Professor Wilcox conveniently out of state, Dellaroche and Anderson search her office at the Fu Institute, uncovering a wealth of mathematical research that raises more questions than it answers. Meanwhile, Stevens and Smith discover the hypergeometric sequence has already begun infecting the Alliance Police Department, where officers have descended into obsession and conspiracy theories.

Stevens and Smith examine the evidence recovered from the case, uncovering unusual data on Michael Wei’s phone and Fitbit that makes his final days even harder to explain. Meanwhile, Dellaroche and Anderson trace the murder weapon to an NYPD precinct, but finding where it came from proves much easier than finding out how it reached Wei.

As Anderson digs deeper into the subject of Wei’s PhD, Smith becomes increasingly consumed by the numbers and hidden code recovered from Wei’s phone. Meanwhile, Dellaroche and Stevens stake out a property in Newark, where what begins as routine surveillance uncovers something far beyond anything they expected to find.

While Stevens and Dellaroche work to stage the Newark safehouse and erase all trace of their involvement, Smith continues to purge the last of the sequence from FBI evidence - only to find someone has already had a peek. Meanwhile, several late-night contacts draw Anderson deeper down a rabbit hole, as he is drawn further into a different investigation.