James narrates the beginning of the movie, explaining what is going on and who the people are. There appears to be a strong wind blowing debris but it is a weed eater cutting grass.James is celebrating his 29th birthday with his family in Wales. He has terminal cancer and must walk with a cane and take morphine and other medications.Davy has been declared redundant by a PR firm and must live with the family of his wife Chloe, James' sister. Chloe isn't happy, and they have children.Bill planted a tree which will be taken for permanent relocation to a favorite place on the coast that James wants to visit one last time. The audience later learns Bill's girlfriend is pregnant and while he acts immature, he is very concerned about his ability to be what his girlfriend needs him to be.Miles is an aspiring writer but not successful yet. His father, a successful writer, died of cancer.After the party with the family the four men are ready to go on their long journey to Barafundle Bay in Pembrokeshire. Bill is told not to take his guitar. The journey starts in a vehicle but eventually the group must walk to their destination which will require four nights of camping. A cart carries all their stuff, and since James can only walk so much, it must carry him as well.Early in the journey the group stops at an event which includes music resembling what Americans call bluegrass. Miles visits the restroom along with a young boy wearing angel wings who is no angel. He realizes his watch is missing and goes in search of the boy. The boy is quite rude and starts to give the watch back but ends up throwing it in the water. Miles doesn't try to retrieve it but returns to the event, where a fight starts. The men all get involved, even James (he seems to be enjoying it) and then they run away,The first couple of nights camping include nonsensical fun. The journey also includes treating the cart like a sled on a long hill.To get to where they are going, the men must take a ferry. The ticket seller is somewhat quirky and the men have to negotiate to get a fair price.Once on the other side, the men visit a rocky beach where a man is searching for treasure. As the man explains it, he met a Chinese sailor in France who claimed he lost a shipment of valuable Star Wars memorabilia. The items should have washed up in the area where the man was searching, and he had already found items with sell by dates indicating they were from the same time.As the group prepares to camp once again, James tells Davy he can't get up and needs his medication but doesn't want to tell the others. Over the next couple of days, there are discussions of what happens when we die and whether there is a God, and confessions made to some or all of the group. Miles wants to be with Chloe, and Bill finally admits his girlfriend is pregnant. James has read Miles' first novel and was impressed.There is one scene with wild horses, where one of the men refers to the Third Star which is a guide to a destination, the one reference to the movie's title.Before they arrive at their destination, the group must use a rope to go down a long hill. One of the men has to carry James.There is a discussion about whether to extend the vacation, but Miles says he must get back to work.James has a bad episode and it is suggested they give up. James is determined to keep going.On the fourth night of camping, the men set off fireworks. One goes in the wrong direction, setting a tent on fire. All four men must now share one tent. Also, James is in terrible pain and his medication cannot be found. Two of the men go back to where they were before to see if it fell out. It did, and they bring it back.At last the destination is reached. James realizes it's not the place he thought it was. Nevertheless, the men all go in the ocean. The tree that was supposed to be planted is no longer with them, after an argument earlier.The men start their journey home. During an argument after Miles' phone rings, since they were hoping to be out of touch, the cart goes over a cliff. The men still have most of their stuff but now they must carry James. Miles has explained his work requires he stay in touch.James is realizing the rest of his life will be nothing but pain and medication. He wants to go in the ocean and for the others to just leave him there. They don't want to do that, but eventually they do.James narrates the end of the movie.