Vikings returns for a gripping fourth season. Season three culminated with the extraordinary battle in Paris, where Ragnar seized victory from the jaws of defeat, but still returns to Kattegat dangerously ill. Thoughts of his death galvanize the forces who seek to succeed him as king, including his wife Queen Aslaug and his oldest son, Bjorn. Meanwhile, Lagertha continues power struggles with her calculating, former second in command, Kalf.