Working to reunite former Federation member worlds, Captain Burnham and her crew rush to provide emergency aide to a space station that has been sent hurtling through space. On Kaminar Saru works for his people as an elder statesman, but longs to return to the stars.

When Discovery attempts to retrieve sensor readings on a massive anomaly threatening the Federation and its allies, Michael and Book clash over his fitness to fly a dangerous mission into the heart of the anomaly.

With help from Michael's mother Discovery attempts to apprehend a member of the warrior caste Qowat Milat, who has killed a Starfleet officer and stolen a shipment of dilithium. Gray puts himself on the line to start a new life in an android body.

Lt. Tilly agrees to lead a group of Starfleet cadets on a team-building exercise, only for their shuttle to crash on a frozen moon. Burnham and Saru join the Federation delegation to Ni'Var, where plans for their rejoining the Federation go awry.

After the anomaly jumps a thousand light years Discovery leads a rescue mission to evacuate a chain world now in its path. Meanwhile Stamets bristles when a brilliant scientist comes on board the ship to crack the anomaly's secrets.

Discovery's crew enters the spatial rift left behind by the anomaly in the hopes of finding a clue to its origins, leading to a crisis for the crew – and for Zora, the ship's emerging artificial intelligence – when they are unable to escape.

Michael faces an unexpected challenge when Discovery's sentient computer discerns the origins of the D.M.A. ... but refuses to disclose it to the crew. Meanwhile the Federation hosts representatives from dozens of worlds in an effort to coordinate a response to the anomaly.

After Book and Tarka go after Species Ten-C Captain Burnham is tasked with hunting them down, leading to the criminal underworld where she and Book used to run – and a race to acquire a deadly weapon.

Discovery chases Book and Tarka to try and stop them from attacking the D.M.A., forcing Michael to put her crew on the line for a mission that might kill the man she loves.

Discovery's mission to make first contact with the creators of the D.M.A. forces them to attempt to penetrate the Galactic Barrier at the edge of the galaxy. Elsewhere, a trip to Tarka's former prison reveals his true motives to Book.

Burnham leads an away mission to try and learn more about Species Ten-C to aid in first contact, while Book and Tarka arrive and attempt to infiltrate Discovery in secret.

With the D.M.A. threatening the heart of the Federation, Discovery's crew attempts to make contact with the advanced alien race that created it – before it is too late.

After Tarka attacks the Ten-C Discovery works to reestablish first contact, while Earth and Ni'Var scramble to evacuate as many people as they can from the DMA's destructive path.