The Border opens with a bomb attack which kills officers from a Border Guard unit deployed in the Bieszczady Mountains. Only one of them survives. Captain Rebrow loses his friends and his beloved Ewa in the attack. Shattered, he tries to get to the bottom of the assault and find out who is the mastermind behind the bombing.

DA Iga Dobosz is heading the investigation into BG station bombing – she interrogates Major Markowski and Michał Łuczak, Rebrow’s friend. Rebrow decides to accept Markowski’s offer and return to active service. Markowski agrees on two conditions: Rebrow must not conduct his private investigation into the bombing and being a suspect he must remain at the DA’s disposal.

DA Dobosz is interrogating Grzywa. Grzywa reveals that Rebrow is in trouble with Kalita, and this is the man the DA should be talking to instead of harassing honest people.

The case turns out to be more complex than it appeared to be. Everything indicates that Ewa survived the explosion and was hiding in the forest for weeks. DA Dobosz finds a small key in the jacket Ewa was wearing. She decides to call in Grzywa once more for interrogation...

The police are searching a murder scene to preserve the evidence. DA Dobosz finds Rebrow’s lighter (with an engraved wolf) lying in the grass and later interrogates all people who were the last to see the victim alive. She talks to Markowski and Rebrow. She has some questions to Grzywa, but no one knows his whereabouts...

The funeral takes place in Warsaw. The coffin is flanked by Border Guard officers forming the guard of honour. After the funeral, DA Dobosz meets with the Vice-Minister who provides her with new evidence vital to solving the mystery of the guardhouse bombing...