Graham has to take the helicopter out to search for a reckless snowboarder in danger and, because Graham has promised to spend the afternoon with his daughter, Zoe and Lassie set out with him. While the rescue mission is not what she is expected of the afternoon, Zoe discovers her inner sense of duty, like a true ranger.

When a mysterious epidemic breaks out in the park, Zoe is determined to find out what has caused it so that Lassie and other animals don't fall ill. Zoe soon loses patience with Harvey's scientific approach and his insistence on seeking out proof.

Impatient to see her friend Judith again, who has left the valley several years hence, Zoe reminisces about their intrepid adventures in the Park. But their reunion takes an unexpected turn for Zoe when she discovers her friend is now confined to a wheelchair.

When Mrs. Lee opens a letter that Zoe, Harvey and Lassie bring her, she learns that she is the last living heir to a former mining concession. When Mrs. Lee lets them read her journal from the period, the kids and Lassie set out in search of the abandoned mine to discover the "magnificent treasure" that the journal hints is hidden there.

When Lassie spectacularly rescues a herd of escaped zebras, a circus director is so impressed by her performance that he insists that Lassie join his troupe. Naturally, he comes up against Zoe's refusal: Lassie is not a circus animal; she is a member of the family. When her beloved Lassie disappears, Zoe is convinced that the circus director is behind the disappearance.

To perpetuate his father's own passion, Harvey decides to enter the photo competition for the Park's Visitor's Guide. When he finds out about his rival - Samantha's- high-tech equipment, Harvey asks Doctor Dudley to tweak his camera to be able to take spectacular photos, even if it means putting himself in danger.

Zoe, Harvey, Graham, Beth and Lassie are forced to interrupt their hike on the valley glacier when they notice that its peak is in danger of collapsing. Beth seems hugely upset at the idea. Later, when Lassie notices Beth's car parked at the foot of the glacier, Harvey realizes that his mother has been hiding something from him. Despite the danger, he sets out to look for her with Zoe and Lassie.

Zoe and Harvey set out to investigate theft from the park archaeological site. The pair soon finds themselves in big danger and Lassie is faced with a huge dilemma when she finds she cannot save both of them. Lassie has to use great cunning and aplomb to save the kids from their predicament while also putting a stop to the thefts.

Harvey's father was a famous rock climber who died when Harvey was just a baby. When a Park event leaves Harvey feeling the loss of his father very strongly, he sneaks away from the Valley to make the dangerous climb to a remote lake that was his father's favorite spot in the world. Guessing where he's gone, Zoe, Lassie and Harvey's mother, Beth, hike after Harvey, hoping to catch him before he gets into real danger. In the end, Harvey's own gifts and Lassie help the boy reach the remote lake and share a moment with his father.

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.

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...

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.

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.

Following Mrs. Lee's indications to find a special flower which may cure Biff, Lassie and the kids look for the home and garden of an aging hermit named Frances. The old woman seems mean and inaccessible and when the kids unintentionally infuriate her, they look like they may be in trouble. Things change when Lassie gives the kids some insight into Frances' true nature and they realize they're perfectly situated to help the old woman find a way to happiness.

When Zoe and Harvey visit the new dam at the edge of the park, the noises emanating from the construction upset Lassie who refuses to go any closer. When she understands the valley can be flooded due to Nick's error, Lassie has to draw on her inner strength to overcome the stress the sounds of the dam are causing her and save the kids trapped inside the dam.

Zoe and Lassie take Harvey up a small creek to see a beaver dam and visit her family's favorite swimming hole. Realizing that the beavers - and the Creek itself - are threatened by a pair of unscrupulous gold miners who have snuck into the area, Zoe and Harvey take in on themselves to stop them.

Zoe and Harvey must ignore an oncoming storm to help a group of amateur tornado chasers survive outside in the dangerous weather. Luckily, with Lassie to help them, the odds are on their side.

Zoe and her mother nurse an injured Grizzly cub back to health and release it into the wild. However, when Zoe realizes she may have just handed the little bear over to a poacher, she, Lassie and Harvey head back into the forest to set a trap for the poacher and rescue the cub.

Thanks to Lassie, the children avoid a landslide on the hill overlooking the visitor center. Looking down they realize the building has been damaged. With the center now closed for safety reasons, Beth has no choice but take new work away from the park.

Skiing in a local resort, Zoe, Lassie and Harvey meet a reckless young teenager named Drew. The supremely confident older boy convinces the kids to try a run that Graham has recently closed because of the danger of avalanches. The run is steeper than Drew can handle. His thirst for excitement puts him as well as Lassie and the kids in danger. But as the kids work their way into the back country to find Drew, they find themselves face to face with a hungry wolverine... right in the middle of an avalanche zone!

Zoe and Harvey witness a lightning strike that begins a forest fire. Making a heroic choice not to head for home, Zoe leads Lassie and Harvey up the mountain to a fire lookout, using the radio inside to alert her father to the fire. However, her eagerness to save a group of animals trapped by the advancing fire puts them all in danger.

Zoe, Lassie and Harvey are with Graham in a nearby town when Sarah calls them with an emergency. Mrs. Lee has been bitten by a poisonous spider and needs antivenin. Rushing home, Graham and the kids encounter a couple of tourists who have got themselves into trouble. Graham is duty-bound to remain behind. Now it's up to Lassie, Zoe and Harvey to find the quickest way into the valley... and that means rafting down the notoriously dangerous rapids.

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.

Zoe, Harvey and Lassie take a dangerous trip into the forest to find Zoe's beloved Aunt Kim, who has crashed her plane in the high country. What Zoe doesn't know, is that Kim was carrying a cougar in a cage - and finding Kim means walking into danger.

It is rare that wolves will attack livestock, so when local Rancher angrily report that their cows are being killed by a vicious wolf, Sarah decides to head into the back-country to figure out what's really going on. With Zoe, Harvey and Lassie along, Sarah hikes into the high country to observe the wolves and see if the Ranchers' accusations could be true. When she discovers the real culprit, Sarah and the kids find themselves in a dangerous situation and only Lassie can save the day.

It’s "Adopt-a-Puppy" day and Zoe and Harvey host Olive and her father who have come in search of a new family friend. But the puppy Olive falls for does not turn out to be as courageous and Lassie-like as her father would have liked. Zoe relives the first time she met her beloved dog, at the same time as her best friend Harvey, who had just arrived in the valley!