Ragnar warns Floki about the price he must pay because of his actions. In the meantime, Rollo finds an ally in Count Odo.
Mercy is the third episode of Vikings season 4. Why does the episode carry this name? Because of the visions that Ragnar and Ecbert experiment about Athelstan, begging for mercy.
Meanwhile in Paris, Rollo endures to learn French, as he's mistreated by his wife Gisla. On the other had, Kalf reveals Lagertha he's in love with her, although she doesn't feel the same. After, Kalf will send a Berserker to kill Bjorn.
Also, Ragnar frees Floki, as he comforts Helga by telling her that she already suffered enough. In the meantime, Wessex keeps preparing its soldiers, and Aethelwulf returns after rescuing Kwenthrith and Magnus.