The last episode of Vikings season 4 ended with Ragnar's fleet getting destroyed by the storm leaving Ragnar and his crippled son Ivar drowning at sea. Unsurprisingly, both Ragnar and Ivar survive the storm and arrive at Wessex as shown in the teaser video for the next episode.
Ragnar, the once respected king of Norway has fallen from grace with his recent defeat at Paris and his secret of the massacre of his settlement in England being revealed. Now Ragnar wants to exact revenge to the rulers in England for the massacre. The problem is, nobody respects Ragnar anymore and thus he was forced to bribe people to come with his expedition to England. The misfortunes continue when a storm ravaged Ragnar's already small fleet. Vikings season 4 episode 13 will continue the misfortunes as Ragnar's death is imminent according to history books.
Based on the history of Ragnar, the famous Viking will be captured by King Aelle and be executed by being thrown in a pit of snakes. Ragnar's death occurs in England, which coincidentally is where Ragnar will end up to on Vikings Season 4 Episode 13. If Vikings Season 4 follows Ragnar's history, we might see his death by the end of the season. However, if Vikings Season 4 Episode 13 chooses to diverge from history and prolong Ragnar's time, then we will see him exact revenge on England with the help of Ivar and possibly become King of England.
Meanwhile Bjorn, eldest son of Ragnar has his own expedition to the Roman Empire but needs to pass through his Uncle Rollo's kingdom of Paris. In the first half of Vikings Season 4, Rollo was a tragic character who always lived under the shadow of his more famous brother Ragnar. But now despite his betrayal of his country, he has since surpassed Ragnar and defeated him in combat and is now the rightful ruler of Paris. In the teaser video, we see Rollo on board the ship of Bjorn which suggests that Rollo is helping his former brothers. Vikings Season 4 Episode 13 has now added some intrigue as to where Rollo's true allegiance is. My money's is on he's sticking with Paris since he only had a feud with Ragnar and not his nephew in Bjorn.
Back at home in Kattegat, we see Lagertha waging war with Aslaug to reclaim her throne as queen on Vikings Season 4 Espide 13. Lagertha and Aslaug never got along from the beginning as Lagertha claims Aslaug stole Ragnar from her. In the teaser video, we see that the war has already started. Fans generally like the brave shield-maiden Lagertha more than Aslaug. But with Ube and Sigurd protecting their mother Aslaug and, expect Lagertha to be defeated and maybe killed. The sons of Ragnar have more potential stories than Lagrtha so expect Lagertha to loose the battle.
Then again these are all speculations based on history and logical choices. Stay tuned for Vikings Season 4 Espide 13 to find out.