A/N: Terror of the Zygons is my favorite episode ever, but Harry's send-off was a bit of a letdown. I always thought it should've been a little more heartfelt. Especially given the fact that anyone with eyes could see that Harry and Sarah totally liked each other, what with all their arguing/flirting in Season 12.

At one point in the episode, Harry mentioned that he and Sarah walked back from Forgill Castle together, and that it was "a very long walk." What do you suppose they talked about during that very long walk? I imagine it went something like this.

"Sarah, we're wasting time." Harry was already headed for the door.

"Agreed, agreed." Sarah gave a reluctant sigh and followed him outside.

When they got outside, they both suddenly realized a little detail they had overlooked when they asked the Brigadier to drop them off at Forgill Castle.

They exchanged sheepish glances. "So how are we going to get back, then?" Harry voiced the question on both their minds.

"I guess we're walking." Sarah said with a shrug.

They set off together, walking at a comfortable pace. Sarah glanced over at her comrade. "Are you sure you're up to all of this, Harry?" she asked, concerned. "All this running about, chasing Zygons and whatnot? It's only just yesterday you were hurt."

Her gaze shifted to the wound above his left eye. He was lucky that the bullet had only grazed his skull. She suppressed a shudder, realizing that had Harry's attacker aimed just a little bit more to one side, the shot could have easily killed him.

All this crossed her mind in the two seconds that passed before he answered. "Well I don't really seem to have a choice in the matter, do I?" he sounded annoyed. "I just keep getting caught up in these insane adventures. I haven't had a say in any of this since I stepped into the TARDIS back at UNIT HQ. It's been full-speed ahead ever since then."

Sarah regarded him seriously. "Do you regret coming with us?"

He sighed. "No. I'm sorry. I—I didn't mean to sound that way. I'm just tired is all." His eyes confirmed it. The spark of boyish, optimistic energy that usually illuminated his deep blue eyes had faded to a glimmer, half-hidden beneath an unearthly sort of exhaustion. Sarah thought she rather missed that sparkle.

"I really have enjoyed traveling with you and the Doctor." Harry added. "It's been wonderful, it really has."

Sarah raised her eyebrows. There was something in his tone….."But?"

"But it's all too much for me. The Wirrn, the Sontaran, the Daleks, the Cybermen, and now the Zygons." He ticked each one off on his fingers. "Every time we get done with one adventure, we're off on the next one just like that." He snapped his fingers for emphasis. "We've hardly had a moment's rest since we started out."

He stopped and turned to face her. "When this Zygon business is cleared up, when you and the Doctor leave in the TARDIS…..I won't be going with you."

Sarah nodded solemnly. She didn't look too surprised. "We'll miss you, Harry."

"I don't think the Doctor's going to miss me much." Harry said with a little laugh, starting off again.

Sarah followed him. "Oh he likes you." She insisted. "He's just a bit…..moody sometimes."

"You didn't hear him call me and imbecile when we were on Voga." He said quietly.

"No, but I did hear what he told you on the Ark."

He looked at her quizzically.

"On Nerva. The first time we were there." She explained. "Just before the transport ship was launched, when the Doctor thought he was about to die, I heard him tell you to look after me. I'm not of the opinion that I need looking after, but the Doctor wouldn't have told you to unless he really trusted you."

"I suppose that's true." Harry consented. "I hadn't thought of it like that before."

They walked on in silence for a few moments. Harry reached in his trouser pocket and withdrew a crumpled up bit of paper.

"I've still got my train ticket." he turned it over in his hands and smoothed it out as best he could. "So I guess I won't have any trouble getting back to London."

"Well a train is certainly more reliable than the TARDIS." Sarah agreed with a little laugh. Then she sobered and looked at him. "Oh Harry, do you have to leave?"

He nodded sadly. "I think it's about time I bowed out gracefully."

It was Sarah who stopped this time. "It's just—" she bit her lower lip hesitantly. "I like you, Harry. A lot. And I like having you with us."

Harry took her hands in his. "I like you a lot too, Sarah." He said earnestly. "But I'm just not cut out for this sort of thing. I don't regret it. I'm glad I went along. I've seen a lot and learned a lot….and I've been able to help people in ways I never thought imaginable, and I think I'm a better man for it."

He released her hands and turned and stood, hands clasped behind his back, at the edge of the path, where it sloped down and ran into a deep valley. Beyond the valley, the rolling Scottish hills stretched out as far as the eye could see. A gentle breeze swept in and ruffled his light brown hair.

"But my place is here, on earth." He said.

Sarah came and stood beside him. He looked at her out of the corner of his eye. "There's a lot of good I can do on earth." He explained. "There's lots of ways I can help people here. All sorts of medical advancements that no one's even thought of yet. If there's one thing I've learned from the Doctor, it's to dream big. Nothing is impossible!"

As Harry spoke, Sarah could hear the excitement creep into his voice, and the sparkle that she so greatly missed began to return to his eyes. Seeing it, she couldn't help but smile, and some of her sadness evaporated. It wasn't just that he wanted a break from all their adventures, then. He really wanted to start making a difference right here on earth.

A few moments passed as they stood in companionable silence. It was Harry who finally broke it.

"We really ought to be getting back. After all," he grinned and offered her his arm. "We've got a world to save."

Sarah returned his smile and took the offered arm, and they resumed walking.

"These big things you plan to do," Sarah said. "Any ideas where you want to start?"

"I've been thinking a lot about preventative medicine." Harry replied thoughtfully. "Maybe vaccines."