When Zoe and Harvey make a bet who can get home first, they take different paths. While Harvey follows the paths as indicated on his map, Zoe attempts to blaze her own trail. But without Lassie along to guide her, Zoe will get herself hopelessly lost.
When Sarah must head into the field to investigate an illness that is affecting the park's deer, Zoe is left in charge of the one fawn that appears to be resistant to the disease. When the little deer escapes, Zoe feels responsible and sets out to find him, taking Lassie with her.
Robert Humphrey begins running steam-train tours in Grand Mountain which Lassie and Zoe see are scaring the park's small herd of buffalo. Graham tells Humphrey he must change the train's route. Humphrey ignores the warnings and sends the train down an old and damaged track. Now, not only are the buffalo in real danger, but every passenger on the train is at risk... and only Zoe and Lassie can prevent a disaster.
After Lassie spots a condor that's been hurt in the wing, Zoe and Harvey must transport the endangered bird to Sarah's clinic. Lassie realizes the Condor has left a chick in her nest and the kids realize they must save TWO generations of this endangered species. With fewer than 400 of these rare birds left alive, their mission is a vital one.
Zoe's father Graham grew up in the Valley. His grandparents were some of the area's first residents. While Zoe knows a lot about her family, one mystery remains: there is a tiny valley where her father used to go that he never talks about. In fact he's never revealed its location. Harvey figures out where the valley must be and he, Zoe and Lassie hike in to discover the truth about the spot.
The Grand Mountain Adventure Challenge is an annual contest for kids. The Challenge tests kids' abilities in canoeing, hiking, rock climbing and orienteering - and this year it has a 10,000 dollar prize. The unprincipled coach of one team kidnaps Lassie in hopes of taking Zoe and Harvey out of the race, but he has underestimated the kids' friendship with the other competitors, who join in the search for Lassie. And he has also severely underestimated Lassie's own resourcefulness and ability to escape. Zoe, Harvey and Lassie return to the starting line just in time to begin the race.
The Grand Mountain Adventure Challenge begins with Zoe and three other teams competing. From the beginning, things begin to go wrong for each of the teams. One by one, each of the other competitors gets into some kind of trouble and Zoe and Harvey have no choice but to put their own progress on hold while they save their friends. They discover that these mishaps were no accident and come to realize that one team is cheating...
Marty and Jeannie come up with different approaches on how to deal with Lukas' attempts to sabotage DollaHyde. Meanwhile, the relationship between Roscoe and Lex becomes a problem for Marty.
With German goods being taken off the store's shelves, Harry organises a patriotic concert to raise money for British troops, and Lady Mae arranges for an old friend to headline the event. However, Harry has also offered to help the government, and just as the gig is about to begin, he's ordered to leave London on a secret mission to Berlin. Elsewhere, Agnes and Victor find themselves going over old territory and an increasingly paranoid Thackeray takes action against Henri.
Just when Rick thinks he's going to be able to relax, he's faced with multiple immediate threats. Other members of the group deal with their past.
Jeremy Clarkson heads to Italy to get behind the wheel of the exclusive, hand-crafted Touring Superleggera Disco Volante, which is based on the already rare Alfa Romeo 8C Competizione sports car. Richard Hammond asserts authority over the sand dunes of Abu Dhabi in the six-wheel-drive Mercedes-Benz G63 AMG 6x6. James May defies his status as Captain Slow by blasting two Caterhams around the test track - the minimalist entry-level Seven 160 and the full-fat supercharged Seven 620R. Comedian Jack Whitehall sets a lap time in the Reasonably Priced Car.
Tom, the local curate, asks Trixie to join him for a day of cricket. She accepts, but the date is disastrous. Shelagh decides to talk to Dr. Turner about adopting a baby. Patsy, struggling to adapt to the unpredictable and chaotic life that midwifery brings, upsets a young mother in the clinic.
Dom's feelings for Lynn grow as they discuss becoming business partners, a frustrated Agustín introduces CJ to Frank, and Patrick introduces Richie to his friends at Dom's 40th birthday party.
Porthos wakes up after his drunken birthday celebrations with a dead body next to him. The Musketeers must prove his innocence as he gets sentenced to death.
Danny is excited to team up with Vanessa for a school project, but when Vanessa’s mom overhears The Cannon’s expletive-laden rant, she tells her daughter to request a new partner.
Terry tries to help a love-struck Lulu catch the attention of Patrick, the new doctor in town...but it seems he has more in common with tomboy Terry than with girly Lulu.
At Malcolm's funeral Cleaver meets Mal's sister Felicity, a honey blonde with an acid wit; and baulks at being Scarlet's junior in the case of a gambling-addicted client.