So you can pay attention to Donaldson try to change his drawl into something that passes as 9th century Norse, I thought I'd give you a bit of a rundown of a few things have changed in Season 4.
King Ragnar and his band of vikings raid Paris. It goes well.
Ragnar heads home but leaves his brother Rollo behind to protect their interests.
Rollo instead marries a French princess, becomes the Duke of Normandy and cuts his hair. This is from a much earlier episode, when Ragnar made him get baptised to appease the English people they were negotiating with. It's always cracked me up.
Anyway, Ragnar and company return to France and get their asses kicked by Rollo's army. Ragnar, upon returning to Scandinavia, disappears for a decade.
In that decade, Ragnar's sons become men:
Bjorn, his oldest, is his son with Lagertha.
Next are his sons with Aslaug:
It's sometimes hard to tell the Aslaug sons apart, especially the middle two, but here is a cheat sheet:
Ubbe is the most reasonable, looks the most like Ragnar. He's too soft, according to Ivar.
Sigurd has 80s hair band hair. He's too soft, according to Ivar.
Hvitserk has brown eyes. He's too soft, according to Ivar. (I actually don't know if Ivar think Hvitserk is too soft as he's never actually said it, but he probably does.)
Ivar the Boneless is the most memorable. He can't walk (hence the boneless name), so he drags himself on the ground or gets piggy backs. He's also crazy, matched by his crazy blue eyes.
This is a family meeting they have before Ragnar returns.
This is the basic rundown of what has happened in Season 4B:
Bjorn decides he wants to explore and plunder the Mediterranean. Bjorn takes a bunch of men, including Hvitserk, his younger brother, and Floki.
Ragnar and Ivar head back to England.
Ragnar is executed (in a pit of snakes) by an English king.
Meanwhile, Lagertha, Ragnar's first wife, invades Kattegat and takes it over, apparently in revenge for Aslaug, Ragnar's second wife, seducing Ragnar and stealing her kingdom.
Ubbe and Sigurd are pretty mad, especially since Lagertha killed Aslaug in the process.
Ivar returns from England, is angry that that his mother has been killed and that his brothers haven't killed Lagertha yet.
Word comes to all of Ragnar's sons, through visions of Odin, that Ragnar is dead.
Ivar is angry and wants to kill Lagertha to avenge his mother. Ubbe, Sigurd and Ivar all challenge her in the throne room before Bjorn returns.
They all decide that they will band together to seek revenge in England for the death of Ragnar and then maybe deal with the other issue later.