The desert that summer was harsher than anyone could remember.

For weeks, the sky had remained a pale, merciless blue, without a cloud large enough to cast a shadow. Wind rolled across the plains like a living thing, dragging curtains of dust behind it and stripping the color from everything it touched. The grass had disappeared almost entirely. The few surviving patches were yellow and brittle, crushed beneath the hooves of passing horses.

Even the mesquite trees looked like skeletons.

Their branches reached toward the empty sky, thin and twisted, while their leaves had curled inward to protect what little moisture remained in them.

For the Apache band moving across that country, every mile had become a battle.

Their water bags had run dry the night before.

The horses staggered beneath their riders, heads hanging low. Some of the younger animals had begun to stumble. The children were too exhausted to complain. Their mothers carried them when they could, but even the strongest women were weakening under the relentless heat.

At the front of the group rode Chief Hosa.

He was an older man, broad-shouldered despite the years that had passed over him. Silver had begun to appear in his dark hair, and a long scar crossed the back of his right hand. He had spent most of his life learning how to read the land, yet the desert offered him nothing now.

No birds.

No green growth.

No distant glimmer of water.

Nothing.

Behind him traveled twenty-two families.

They had been forced to move after a combination of drought, sickness, and repeated attacks made their former camp impossible to defend. Their supplies had dwindled. Their horses had weakened. Two elderly people had died during the previous week, and several children had fallen sick.

Hosa had tried to hide his fear.

A chief could not afford to let his people see him surrender to despair.

But that morning, when he looked back and saw his granddaughter being carried by her mother because she could no longer walk, something inside him nearly broke.

He turned forward again.

"Keep moving," he said.

His voice was steady.

The people obeyed.

But everyone knew the truth.

They were running out of time.

Nearly thirty miles away, a cowboy named Caleb Mercer was having a bad morning for entirely different reasons.

He had spent the first hours after sunrise tracking a herd of mustangs that had scattered during a thunderstorm several days earlier.

The storm had been brief but violent. Lightning had struck somewhere north of the plains, and the frightened horses had broken through a temporary enclosure and vanished into the wilderness.

Caleb had followed their tracks for two days.

He wasn't searching for adventure.

He wasn't looking for trouble.

And he certainly wasn't searching for people.

Caleb had spent most of his adult life avoiding all three.

He was a quiet man in his early thirties, with sun-browned skin, dark hair, and a weathered face that made him appear older than he was. He owned a small ranch several miles from the nearest settlement, where he raised horses and occasionally took work as a guide.

He had learned long ago that the frontier rewarded patience.

It punished foolishness.

And it killed men who believed they understood everything.

That morning, he found the mustang tracks again.

They led west.

Caleb followed them until the trail climbed toward a rocky ridge.

When he reached the top, he pulled his horse to a stop.

Something caught his attention in the valley below.

At first he thought it was a herd of cattle.

Then he saw people.

Dozens of them.

Moving slowly across the open ground.

Caleb shaded his eyes.

Apache.

He recognized them immediately.

His first instinct was to turn away.

Not because he hated them.

Because he understood the danger of getting involved.

The frontier was full of old wounds.

A man could do something with the best intentions in the world and still find himself caught between people who had been fighting each other for generations.

Caleb watched the group for another minute.

Then he noticed how slowly they were moving.

Too slowly.

He saw a child being carried.

He saw men riding with their heads bowed.

He saw women walking beside nearly exhausted horses.

And suddenly Caleb understood.

They were dying of thirst.

He had been thirsty enough times to recognize desperation.

There was a particular way people moved when water became more important than anything else.

Caleb had seen it in cattle.

He had seen it in horses.

He had once seen it in a trapped miner who had gone nearly three days without drinking.

He could not ride away.

"Come on," he murmured to his horse.

The animal turned reluctantly.

Caleb looked toward the west.

He studied the canyon walls.

The color of the earth.

The shape of the rocks.

The vegetation—or rather, the lack of it.

Something about the land bothered him.

Then he remembered an old story.

Years earlier, his father had told him about a hidden spring somewhere in these hills. The old man had never found it himself, but he had learned about it from a prospector who claimed that water existed beneath a narrow break in the stone.

Caleb had never believed the story.

Until now.

He rode west.

The farther he went, the more carefully he studied the ground.

At last, he saw something strange.

A cluster of green weeds.

Tiny.

Almost invisible.

But alive.

Caleb dismounted.

He walked toward a narrow crack between two walls of sandstone.

He knelt.

Pressed his fingers into the sand.

Then he felt it.

Coolness.

Moisture.

He dug with both hands.

For several minutes, nothing happened.

Then the sand darkened.

Caleb dug deeper.

A thin stream of clear water began to rise.

He stared at it.

For a moment, he simply smiled.

Then he looked back toward the distant valley.

The Apache band was still moving.

Caleb mounted his horse.

He rode toward them.

The Apaches saw him before he reached them.

Several warriors immediately moved to intercept him.

Rifles were raised.

Caleb stopped.

He lifted both hands away from his weapon.

"I found water," he called.

The warriors did not lower their rifles.

Caleb pointed west.

"There is a spring in the rocks."

One of the men stared at him suspiciously.

Then Chief Hosa rode forward.

His eyes moved from Caleb to the distant canyon.

"Water?" he asked.

Caleb nodded.

"Enough for everyone if we move carefully."

Hosa studied him for a long moment.

Then he looked at his people.

"Follow him."

The band moved.

And just before sunset, they reached the spring.

The children drank first.

Then the women.

Then the horses.

Warriors filled the empty water bags.

Some people simply knelt beside the pool and pressed their faces into the cool water.

Caleb stood apart.

He watched them.

He had expected gratitude.

Instead, he saw something more powerful.

Relief.

For the first time in many days, these people believed they might survive.

Caleb turned toward his horse.

He intended to leave quietly.

But Chief Hosa called after him.

"Stranger."

Caleb stopped.

The chief approached.

"You saved many lives today."

Caleb shook his head.

"I found water."

Hosa looked at him.