This was almost as bad as the time last year when River had collapsed, babbling about cracks in walls and suns that were really boxes. She'd been raving for three days, and Simon was very seriously considering something stronger than smoothers, when she suddenly came out of her room and calmly announced that everything was all right, thanks to "something blue".

"The stars are stars again," she had said, before coolly going back to the cockpit and resuming her piloting duties as if she hadn't spent the last three days screaming that they were all dead.

This time wasn't as bad, but it was pretty close.

This time they were right in the middle of dinner when River started to shake.

"It's happening," she moaned, her cup shaking so violently that the hot tea sloshed over the edge into River's lap.

Simon sprung into action, taking the breakable cup away from her trembling hands while Mal pulled the girl, chair and all, away from the table.

"Gorram moonbrain. What's wrong with her now?" Jayne grumbled, reaching across the table to steal River's biscuit. Zoe slapped his hand away, and he scowled at her.

"River?" said Inara in her best soothing tone, crouching down to look the girl in the eye. "What is it, Mei Mei?"

River shuddered violently as another convulsion passed through her.

"Happening," she whispered. "Happening right now."

"Nothin's happenin' right now, Albatross," Mal assured her, looking around the quiet kitchen.

River shook her head, her dark hair flying wildly around her with her erratic movements.

"Demons run away," she giggled hysterically. "Run far, far away. But it'll never be far enough. A good man is going to war."

Mal and Simon exchanged confused glances.

"What is she goin' on about?" Mal asked.

Simon shrugged helplessly.

"That's a nursery rhyme, ain't it?" Kaylee piped up. "Me n' my sisters used to play clappin' games to it when we were kids. Demons run when a good man goes to war."

River let out another hysterical giggle.

"They took what was his. And now he comes to claim it. Coming for all of us. Calling in favours. Building an army. One, two, three, here they come when he calls."

"If somethin's comin', Albatross, I need to know," Mal said.

"Asked for a favour long ago. Now he's coming to collect," said River, as if she hadn't heard the captain.

"Who?" Simon asked, touching his sister's arm so that she turned to look at him. "Who's coming, River?"

"You'd better start makin' a whole lotta sense a whole lotta fast, little one," said Zoe, speaking for the first time since River had started acting up. "Cuz if we're in danger we gotta start preparin',"

River shook her head.

"Not you. Not you who should be scared. Only demons need run," she clutched at her brother's hand, looking him intensely in the face. "Don't you see, Simon? Don't you see? The only water in the forest is the river. Tonight all debts are paid." River stood suddenly, glancing down at the floor, at her bare feet. "Have to prepare. Have to be ready." She bolted from the kitchen, leaving stunned silence in her wake.

"What was that about?" Inara was the first to speak, rising gracefully from her semi- recumbent posture and brushing her delicate skirts.

Jayen shrugged.

"'Sif we know. Girl's off her nut," he took a bite of his protein meal and talked through his full mouth. "She's always sayin' gorram crazy stuff that don't make no sense. Today's no different."

"Maybe I should…" Simon made to follow River out of the kitchen, but Kaylee caught his arm.

"Let her be, Simon. You ain't gunna help her when she's like this. If it's important, she'll come tell us, dong ma?"

"Can we please get back to eatin' now?" Jayne asked, helping himself to River's abandoned biscuit when Zoe wasn't looking.

River was sitting at the bottom the metal stairs in the cargo bay. She was dressed in a dark purple cast-off dress of Inara's, with a heavy gray sweater over top that had once belonged to Mal. Her feet were, for once, shod, sporting heavy army boots. Laid beside her were two wickedly sharp knives and a long-handled axe. She sat quietly, her knees drawn up close to her, silence and unmoving.

A strange grinding sound filled the empty cargo bay, like metal scraping against metal. It echoed in the large space, sounding louder and bigger than it really was. A blue box materialized slowly in the centre of the open space.

River rose, lifting the papery skirt of her dress and strapping the knives to her thighs. She hefted the axe, and walked forward towards the box.

A tousle-haired man with suspenders and a bowtie stepped out of the blue door.

"I've been waiting for you, Doctor," said River.

His lip quirked up in a half smile.

"Then you know why I'm here."

River nodded.

"Calling in favours. And mine's come due."

The Doctor nodded.

"I'm sorry, River Tam. I'm so very sorry. But I need your help."

River smiled at him, a wide, innocent smile that sharply contrasted with the axe she held loosely in one hand.

"The only water in the forest is the river," she said.

The Doctor frowned.

"How do you… never mind. It's not important. What's important is they have my Amy, and I'm not stopping till I get her back."

"I'm ready," said River.

The Doctor stepped aside so River could enter the blue box. As she passed through the doorway, she laid a hand on the wooden frame.

"Hello old friend," said River with a smile.

There was a whirring sound, as if the box was greeting her back.

"Welcome back, Miss Tam," said the Doctor. He reached out and pulled the handle, the door shutting firmly behind them.

The grinding noise started again, the blue box fading from sight.

All that was left in the empty cargo bay was the faint echo of clapping hands, and River's haunting, sing-song voice as she chanted an old nursery rhyme that Kaylee had taught her.

Demons run when a good man goes to war.

Night will fall and drown the sun

When a good man goes to war.

Friendship dies and true love lies

Night will fall and the dark will rise

When a good man goes to war.

Demons run but count the cost,

The battle's won but the child's lost

When a good man goes to war.