History Channel has also released the official plot summary and preview trailer clip of episode 13 titled as 'Two Journeys'. However, the season 5 air date is said to be delayed since the finale episode of the current season will be postponed.
Series creator Michael Hirst shared some details via Mashable on what fans should expect in "Vikings" Season 4B, "I think 4B is would be the biggest season so far; it got the best battle scenes in it. However, it's actually also the most emotional season. All of the major characters end up being changed during the course of this season, so for me, it was digging a bit deeper into the characters and their relationships. It's always been a family saga - it's about families, human beings.
There would be two episodes which are the best I've ever written for TV, and one of them, is totally unusual in terms of the show, in that it mainly involves two characters talking to one another in extraordinary ways."
As for the official plot synopsis of the 13th episode, reports have noted, "King Ragnar Lothbrok's (Travis Fimmel) fleet is shipwrecked and floods the Wessex coast. However, without enough survivors to form a credible force, Ragnar and Ivar 'The Boneless' Lothbrok (Alex Hogh Andersen) have a difficult decision to make.
Rollo (Clive Standen) meets his Viking comrades again and can't resist the urge to join Bjorn Lothbrok's (Alexander Ludwig) voyage, risking his marriage and his new Frank-ish identity. Ragnar is also taking a risk as he brings Ivar towards the Royal Villa in Wessex - putting himself and his son upon the mercy of King Ecbert (Linus Roache). "
For a quick rundown of "Vikings" Season 4B episode 12 titled "The Vision", Entertainment Weekly reported that King Ragnar seek and equipped his voyage to Wessex, even though he's been warned that the gods already left him.
On the other hand, Bjorn prepared to make all his dream to explore the Mediterranean sea come true.
"Vikings" Season 4B episode 13 is titled as "Two Journeys". The upcoming episode is scheduled to premiere on Wednesday, December 14, 2016, at 9:00 p.m. EST first and exclusive on History Channel.
Other than that, the official air date of "Vikings" Season 5 will highly likely be delayed. The finale episode of season 4 will be delayed which pushes season 5 for a fall 2017 premiere.