Mr. Link recruits explorer Sir Lionel Frost to help find his long-lost relatives in the fabled valley of Shangri-La. Along with adventurer Adelina Fortnight, this trio of explorers travel the world to help their new friend.
An explorer named Sir Lionel Frost has always dreamed of making a grand discovery in order to join the Optimates Club, even though they don’t care for him and constantly reject him. When Lionel is invited to find the fabled Sasquatch, he takes a trip and meets the creature, who is actually capable of speech, reading, and writing. Lionel names the creature Mr. Link (and later Susan) and decides to aid him on his quest to the Himalayas where they may find other creatures like him.
The two are joined by Lionel’s old flame, Adelina Fortnight, who uses her late husband’s map to guide them. The heroes are pursued by a bounty hunter named Willard Stenk, hired by the Optimates Club leader Lord Piggot-Dunceby. After evading the hunter numerous times, the heroes reach Shangri-La where they meet a tribe of Yeti, but they reject Susan as they don’t view him as being like them. They keep the heroes prisoner, but they escape after Adelina tells Lionel that he has always been selfish and less concerned with those around him.
As the heroes get away, they are found by Lord Piggot-Dunceby, Stenk, and the former’s assistant Mr. Collick. Lionel tells him off and says he no longer wants any part in the club, and that he regards Susan as his friend. Lord Piggot-Dunceby responds by trying to destroy the ice bridge they are standing on, but the heroes run to the other side as Piggot-Dunceby and Collick fall to their deaths. Stenk tries to kill the heroes for his own ego, but he plummets to his demise as well. The heroes leave, but not before Susan blows a raspberry to the Yeti Elder for being a jerk.
Lionel and Susan part ways with Adelina as she sets off on her own adventure, while Lionel brings Susan back to London so that they may explore the world together.
The film opens with the explorer Sir Lionel Frost (Hugh Jackman) traveling with his partner Mr. Lint (David Walliams) to the middle of a lake. There, they come across the fabled Loch Ness Monster. Lionel lassoes the beast and gets a picture of it, but it then grabs Mr. Lint with its jaws and drags him underwater. Lionel dives in to save Mr. Lint, but the camera is destroyed after the monster whips their boat with its tail.
Upon returning to London, Mr. Lint quits being Lionel’s partner due to the constant distress he finds himself in, as well as Lionel’s obvious lack of care for those he brings along on his trips just for the sake of earning credibility. Lionel looks through his letters and comes across one inviting him to find proof of the existence of the Sasquatch. He then grabs a large stone footprint he came across which he believes belonged to the Sasquatch.
Lionel brings his findings to the Optimates Club, a society of so-called “great men” who devoted themselves to new world discoveries. They have always refused to allow Lionel to join due to his constant lack of proof in his explorations. He speaks to the club’s snooty leader, Lord Piggot-Dunceby (Stephen Fry), and offers to find veritable proof of the Sasquatch. The man breaks Lionel’s footprint and dismisses his claims, but Lionel tells him he is wrong. Seeing that he is being challenged, Piggot-Dunceby accepts Lionel’s wager to join the society if he does find the proof he seeks. After Lionel goes to do so, Piggot-Dunceby tells his assistant Mr. Collick (Matt Lucas) that he is going to hire a bounty hunter, Willard Stenk (Timothy Olyphant), to kill Lionel before he can bring shame to their club.
Lionel travels through Old Kemp Creek to make it to the forest where he discovers the Sasquatch. To his surprise, the creature (Zach Galifianakis) is capable of speech, as well as reading and writing. He brings Lionel to his cave and tells him that he wrote the letter to go find him. He also knows of Lionel due to several unflattering newspaper articles on him. The creature wants Lionel’s help in guiding him to the Himalayas where he believes he will find other creatures like himself, and that way he won’t feel alone. Lionel agrees and figures he must disguise the creature to get him through a crowd. Lionel dubs him Mr. Link, and they head off together. He tells Mr. Link that they will need to find a map kept by Lionel’s old friend, Aldous Fortnight, who has recently passed away and left behind his widow, Adelina (Zoe Saldana).
As the two make their trip, they stop in town for the evening and go into a bar. They are spotted by Stenk and a couple other goons. Lionel knows of Stenk’s reputation for hunting game, but also how the Sasquatch has eluded him. After Mr. Link makes himself known to the crowd, Lionel and Stenk begin to fight each other, which extends onto the rest of the patrons who start to fight one another. Lionel and Mr. Link get away, and they realize they have to keep things moving to avoid Stenk. Later, Stenk sends updates to Lord Piggot-Dunceby about his progress (or lack thereof) and quietly follows the two.
Lionel and Mr. Link make their way to Santa Ana to find Adelina. She and Lionel used to be involved before she married Aldous, and Adelina is less than welcoming to Lionel since he didn’t go to Aldous’s funeral. After Lionel makes it clear he only came for Aldous’s map, Adelina tells him no and sends him and Mr. Link on their way. Later that night, Lionel and Mr. Link attempt to sneak back into Adelina’s house to get the map, but Mr. Link manages to wake up Adelina and her butler when moving the safe containing the map. The butler shoots the safe out the window by mistake, which allows Lionel to grab it and run away with Mr. Link.
The two arrive at the train station in disguise as a nun, but Adelina gets there and easily spots them. Unfortunately, Stenk is also there and has spotted them, and he begins to shoot at the heroes. Lionel tricks him into believing that they hopped onto the train, but he and Mr. Link, now joined by Adelina, get away and hop onto a carriage to their next destination. On the trip, Adelina warms up to Mr. Link and becomes interested in helping him find Shangri-La, where Aldous believed they would find the Yeti.
The trio gets onto a boat, where Lionel warns Mr. Link of what will happen to him if Stenk finds him, in full graphic detail. However, the only concern Lionel has is to win his wager with Piggot-Dunceby. Annoyed at his insincerity, Adelina talks to Lionel in her room about his treatment of Mr. Link. Lionel goes to find Mr. Link outside where he asks him what kind of name he would prefer. Mr. Link recalls of a time when he saw a prospector who smiled at him instead of running away as everyone else does, and he names himself Susan after her. A moment later, Stenk appears and tries to get the heroes, but they fight him off. In the scuffle, Adelina is accidentally knocked overboard but hangs on for her life. Susan goes to save her, albeit clumsily. Lionel manages to evade Stenk once again and gets away on a boat with Adelina and Susan. Stenk reports his failure to Lord Piggot-Dunceby once again, and we cut to him throwing a tantrum.
The heroes travel through India before reaching a town to find a guide named Gamu (Ching Valdez-Aran). They are overheard by Gamu’s granddaughter Ama (Amrita Acharia), who brings them to Gamu’s home. After an awkward few minutes where Susan eats yak-based food and mentions Gamu’s chicken (which Ama warned them not to do), he reveals himself as a beast, which causes Gamu to faint. After she wakes up, she points them in the direction of the mountain where they may find the Yeti. Later on, Gamu’s home is found by Piggot-Dunceby, Stenk, and Mr. Collick, who threaten Gamu’s great-grandson so she can tell them where the heroes are headed.
The trio reaches Shangri-La and are found by the Yeti, who bring them to the Yeti Elder (Emma Thompson). She shows them their land, but they regard Susan as their “country cousin”, and therefore not fit to live among them. The Elder orders her soldiers to throw the heroes into a pit as prisoners. Down there, Susan feels sad that his own kind would reject him, while Lionel continues to grouse about not making it into the Optimates Club, but Adelina tells him off over how selfish he is and the fact that those men don’t care for him, so he has no reason to do so himself. After cheering him up, Susan helps Lionel and Adelina get out of the pit before he climbs out himself.
The three attempt to make their escape, but Susan draws the Yeti’s attention to them, and they chase after the heroes. Outside, they try to run across the ice bridge, only for Piggot-Dunceby, Collick, and Stenk to corner them. Piggot-Dunceby wants to make sure Lionel never brings back proof of Susan’s existence, but Lionel finally tells HIM off on how he no longer cares about joining the club and that Susan is his friend. Piggot-Dunceby then shoots the bridge and starts smashing it to kill the heroes, but his plan backfires, and he falls to his death as everyone runs to the other end. Mr. Collick soon follows. The heroes then hang on for dear life as Stenk stands above them and tries to kill them just for his own pride. Lionel pulls him down, and they begin to slap-fight just as Susan attempts to hold onto an icicle to save his friends. Stenk falls and holds onto Lionel’s foot, but the tip of the icicle breaks off and falls onto Stenk, sending him to his doom. After pulling themselves up, the heroes look back at the Yeti, and Susan blows the Elder a raspberry.
As their journey has come to an end, Lionel attempts to make his move on Adelina, but she decides to set off on her own adventure and to live for herself. Lionel decides to ask Susan to be his new exploring partner, to which he accepts. The two return back to London and head off on their next case. The last we see is a framed photo of Lionel and Susan together as friends.