Sorry for the delay. :) I found that simply tackling this concept was harder than the other parts as all five chapters take place with all Aeldari save Basil. Coupled with work, and I took a while to complete it.

Early 36th Millennium, dawn of the Plague of Unbelief
Within the Webway

Siân Aanwen glanced to her left at Basil. The boy had removed his helmet and attached it to his black carapace armor. Over his shoulder was slung a golden bow she recognized as being of Aeldari manufacture while he still carried an Imperial Force staff in one hand. She watched with amusement as his eyes roamed about the Webway in wonder and she unsuccessfully tried to hide her smile. The child is still capable of looking at the Universe in joyful wonder. The Imperium hasn't beaten that out of him. At least not yet.

The passage through which they walked was little more than a capillary of the great Webway system. A soft light, like starlight surrounded the pair on all sides and yet had no obvious source. The white floor upon which they walked was perfectly smooth, with no discernible breaks or features, and yet supplied excellent footing. On either side of them, the black walls rose above them and then merged into an arch high overhead. The walls also appeared perfectly smooth, yet neither had reached out to verify that the feel matched the look.

Basil glanced to his right into Siân Aanwen's eyes as she glided alongside him, then bashfully turned away. Most humans find us exotically attractive, yet he is too timid to stare into my eyes. The mighty Imperial Inquisitor is too timid, Siân Aanwen laughed to herself before reconsidering. How easily I forget that he is still a boy even after taking into account he is human, still too young to even be considered a young man in many of their cultures. A poor boy who, as a psyker undergoing training to become one of the Imperium's Inquisitors, has most likely had no opportunity to know love or any passion at all, except perhaps hate. Her smile faded away into sadness. "Do you like to dance?" she asked.

The boy nearly stumbled as his toe caught on something unseen. "I don't know," Basil answered. "I have never danced. I remember once, when the Rus Infantry regiment I was stationed with landed on Abalus, some woman came up to the Guardsmen when they were clapping out some tune or other. She started stepping back and forth, then moving her arms and gyrating her hips," he added before momentarily pausing.

He's picturing her in his mind right now, Siân Aanwen realized with a laugh. He probably didn't notice her those years ago in the same way he's remembering her now.

"I think she was inviting them to copulate with her, perhaps for payment of some sort," Basil continued. "Is that what dancing is?" Basil asked. "A prelude to copulation?"

I should be careful of my words as I do not know how he thinks of me or what his designs are. After a moment of consideration, she continued. "In some cases, it is," she answered. "But dancing can be so much more. It is a living art whose performance is as much for the artists themselves as it is for the audience. While those who watch admire the beauty of the movements and coordination…and passion, those who dance are bound together in spirit, as well as body, by the rhythm of the music that they share. Even as some improvise, they, and those who do not, still move in concert to that shared rhythm. That shared rhythm has much in common with…copulation…but, as I stated, dancing is so much more."

Basil simply stared into her eyes as she spoke.

Did the boy hear anything I said? Siân Aanwen sighed to herself, then decided to move the subject along. "Cegorach is the Laughing God. He is our deity of deception, stealth, creativity, art, and trickery. And the Webway is his home," she added. "These passages are to where the Laughing God fled when She Who Thirsts was born."

Basil stared into her emerald eyes, lost for a moment in her alien gaze as she looked back into his, then regained his composure. "Go on," he said. "I've learned so much in such a short time, but I understand there is so much more I do not know."

"Cegorach escaped from her grasp because She could not follow Him here, and even if She could have followed Him, She would never be able to find Him here," Siân Aanwen continued. "The Laughing God has always roamed these walls and He created the Black Library himself. It is the greatest of our craftworlds and the only ones who can come and go freely are the Rillietann, what you refer to as the Harlequins. We refer to those who make the Black Library their home as its Caretakers."

"I've heard the Harlequins term, but little else," Basil answered. "But as to the Black Library, I knew it was a vast repository of information on Chaos but I did not know it was an entire craftworld unto itself. But, please tell me more of the Harlequins."

"The Harlequins are Cegorach's servants and their nature as performers is why I brought up dancing," Siân Aanwen answered. "They are gathered from all Aeldari factions, be they the Exodites who fled into a relatively primitive isolation before our 'Fall', those who inhabit the craftworlds, those who have left the craftworlds such as myself and become outcasts, or even the dread Drukhari, our dark ken. They travel in troupes and masques which meticulously train to perform the great stories of our past and keep them alive, stories told through song and dance. Each member casts aside his old persona and lives that of a part he or she will play, becoming his role. They simultaneously train to become a cohesive and fearsome fighting force which carries out the desires of the Laughing God."

"Are you a Harlequin?" Basil asked.

"No," Siân Aanwen laughed. "I was not so fortunate as to be invited to become a Harlequin, but I was honored beyond belief to have received an invitation from them to study at the Black Library, an honour I could not refuse."

"I take it that is not common," Basil said as the walls and overhead arch vanished, revealing a vast black void on all sides save the white featureless floor beneath his feet. He came to a stop and stared at the expanse for a moment before his eyes noticed and locked onto the small white dots spread across the surrounding void. "Am I actually looking at the stars in the void or is this some sort of image of ancient constellations?" Basil asked Siân Aanwen as he gazed about.

"I honestly do not know the answer to your question," she answered. "There is so much unknown about the Webway and only the Laughing God knows all the answers. I simply acknowledge its beauty and wonder, then move on," Siân Aanwen added. Basil nodded his head in response to her. "As to your question, no, it is not common for Aeldari to be called from their homes for study at the Black Library rather than to join the Harlequins," she continued, pulling Basil's attention away from the surrounding void. "But I am proud to say that Rubha Àird Driseig, the craftworld of my origin, small that it may be, has sent two individuals to study in the Black Library at the Caretakers' request. I studied there not more than three of your Terran Standard centuries ago. While there, I had visions that I would best serve my people by leaving Rubha Àird Driseig and giving aid to the Exodites rather than serving onboard my craftworld and that is where I have spent most of my time since I concluded my studies, all save a short time I spent with some other outcasts, the Aelion Corsairs."

"And the other who received an invitation?" Basil asked.

"His name is Druthact, and he received his invitation from the Caretakers more than three millennia ago," she answered. "He is an ancient and powerful personage of our craftworld who has walked many paths in his long life. He even participated in the construction of Rubha Àird Driseig itself in the years leading up to our 'Fall' and the birth of She Who Thirsts. He is well-versed in passing through the Webway and navigated Rubha Àird Driseig to safety during that tumultuous time when what you Humans refer to as the Eye of Terror was formed from the birth of She Who Thirsts. After he studied at the Black Library, Druthact was not heard from for many long years and only returned a short period of time before I received my invitation to study." She paused and a look of worry momentarily came over her face. And I must find a way to stop him from reaching the conclusion of the game he is playing. At that moment, her eyes were magnetically drawn ahead along the walkway and Basil's gaze followed hers.

Here? Siân Aanwen asked herself in shock.