(wind blowing) (dramatic music) - [Narrator] To film the most mysterious animal in the Rocky Mountains the team relied on the expertise of cameraman Casey Anderson.

Casey is mountain lion-mad, and spends his life tracking them throughout the mountains.

- Of all the animals out there, the one that I'm the most obsessed with is the mountain lion.

If you can get just one moment of watching this animal who's almost impossible to watch, yeah, it's really the biggest payoff for me, the greatest gift ever.

- [Narrator] Casey's tracking skills led him to an abandoned ranch, which he suspected may be visited by a female mountain lion.

- I just walk in here, and it was just 10 times more than I could ever believe.

Every one of these buildings has a dead deer in it, so she's been using these buildings, killing outside of them, caching these deer in here, calling this place home.

And really kind of a dream come true, even though it's kind of nightmarish.

- [Narrator] Casey wants to catch her red-handed as she drags her kills into these barns.

But first, he will need to learn her movements in this vast wilderness.

(wind whistling) Casey, and fellow cameraman Brad Orsted, go into the mountains every day.

They search for prints she may have left behind.

- You can see her tracks right here.

Watch your head.

- [Narrator] They put cameras where she may be sleeping.

- Look at that angle.

- Having the opportunity to follow this cat around such a long time, and really start to develop her patterns and movement.

If I know she's been in here, I know where she's going next.

And if she goes here, she's gonna to go down to the drainage, she's gonna go hunting down towards the ghost ranch.

- [Narrator] Even at night they're on the mountain lion's trail.

After months of patience, the evidence trickles in.

(camera shutter clicking) True detectives, Brad and Casey log every sighting, movement and track.

- It's starting to pay off.

We're really connecting the dots and being rewarded for all that knowledge that she's giving us into her life.

Her pattern is to go that direction, so the ranch could be next.

- [Narrator] But their good luck is about to change.

In the Rockies, hunting is a way of life.

And a mountain lion is a top prize.

Hunters use specially trained dogs to force mountain lions out into the open.

(dogs baying) From his house, Casey hears the sound that he fears the most: hunting dogs.

(engine rumbles) The mountain lion could be in danger.

- Yeah, in America you're allowed to hunt mountain lions.

Predator control.

They're always worried about their livestock, and their livelihood, and they think that the predators are gong to make their lives worse.

(dogs baying) - [Narrator] It's the mountain lion Casey has been tracking.

(lion growls) - Hang tight real quick.

- [Narrator] He sets off to talk to the hunters, leaving the camera behind so as not to antagonize them.

The mountain lion is cornered on the cliff face with dogs blocking her every move.

The only chance the mountain lion has is if Casey can persuade the hunters not to shoot.

The cat's life hangs in the balance.

She's in danger of becoming one of the 400 mountain lions shot in Montana each year.

Casey eventually wins the hunters over, (hunters shouting) and they call off their dogs.

(hunters whistling) (guitar playing) - I laid it all on them, as chummy as I could.

Now they heard me out.

They basically made up their mind that they're not going to kill a cat today.

If we didn't come up here, they easily could have shot her.

Yeah, I feel like I, I don't know, I feel pretty, I don't even know the right word, emotional about it, for sure, because it is life and death.

In the wild, there's so much to worry about.

She's out here dodging wolves and living a crazy life, and then these guys come up here and that could have just, one little moment, it could have been over.

And to be involved in that, somehow getting embedded in that today, to make that not happen, whew, so thankful that that happened, that it worked out this way.

Yeah, pretty heavy stuff.

Like all things, I wish I had a long lens and a tripod.

(chuckling) - [Narrator] But the good news is that at last Casey has concrete evidence that the mountain lion is close by.

(door creaking) - Guess who's back?

It's her.

Getting this footage back and all that hard work and all that speculation that was happening, and then having it pay off right here to prove it that it is our girl, it is our mountain lion, and she's doing this very cool thing in a very cool place, utilizing this old ghost town to thrive.

This is amazing.

This is exactly what we've been busting our butt for, to see this stuff.

See here, she's walking over and giving the camera a sniff.

Yep, it's me.

Yeah, this is the first time that anybody's ever documented a mountain lion in a ghost town.

But I think most importantly she's back, and that proves that she's okay.

And that's the biggest reward of this, by far.