This man is a waste to the fighting profession. He should have met him sooner, when he could have convinced him to be a wizard.

Other wizards dabble in various branches of mathematics, but he always found complex analysis the best tool available.

Cayden has no idea what complex analysis is! Can Gale tell him about it?

At some point in this process it comes up that he can't read. 

He would love to explain complex analysis! (Astarion would like him to shut up about it, but he doesn't count.)

... how has this man been taught topology without learning to read. Has he been cursed, perhaps?

"Never saw much point to it. The party wizard can read the contracts."

...

...

...

"I guess that's true."

Now that rapport has been established Cayden would like to subtly guide the conversations towards topics like "how powerful is Gale?" and "what kind of magic does Gale specialize in?" and "what has Gale's adventuring looked like in the past?" and "civilians: how do you treat them?" and "what does Gale think of women?"

Gale was once fairly powerful! ... not at the moment. Unfortunately.

He's a bit of a Renaissance caster. He could never hold himself to the beauty of just one field. 

He looks Uncomfortable about the adventuring question. He has adventured in the past, and wasn't planning to do it again, but, well, here he is. If he wants to keep his head his own and not explode in a mass of tentacles, he's going to have to take up his staff again.

As someone who has spent most of his life as a civilian, he's very much in favour of them staying in one piece.

His best friend and closest confidante is a woman, and the goddess he follows is a women. Gale Dekarios: pro civilians, pro women.

Cayden makes sympathetic noises about the plight of the teleport wizard, forced to adventure again when all he wants is to be phenomenally wealthy and study complex analysis.

"Who's your goddess?"

"Mystra, goddess of the Weave." Gale wears only a single piece of jewellery, a compass rose ear stud. He can't be sure,  but it certainly looks like a holy symbol.

"Let me guess. She's into magic, discovering new things, and enormous explosions."

He laughs.  "Not so much the latter-- though she isn't strictly against the latter either."

Okay sure he's met Nethysians and he'll believe it when Gale doesn't appreciate things blowing up. 

Making sure that the rest of the party is out of earshot, he asks "Do you know anything about Vlaakith or Shar?"

"I don't know much about Vlaakith that isn't hearsay, but what is said isn't complimentary." He looks a little alarmed. "Why are you asking about Shar secretly?"

"...if you look that alarmed by me secretly asking about it I should maybe keep my reasons secret! I don't, like, have a plan to worship her or anything." Assuming she's not Desna. 

"I would highly recommend not worshipping her. -- You know she's the Lady of Loss?"

"Your planet's gods seem to have almost no overlap with my planet's gods, although I guess I can't rule out that you have fucking, I don't know, Gorum or Abadar or Zon-Kuthon."

"I have never heard those names. --I am glad you asked, at least."

How would Cayden have heard about Shar? There was a limited amount of time between when they were both on the ship and when Cayden rescued him. Lae'zel is unlikely: Githyanki don't go much for gods, and she would be why he's asking about Vlaakith.

This leaves three possibilities:

1. A mysterious stranger

2. Astarion (not exactly the prosocial type from what he's seen).

3. Shadowheart (a known cleric who is wearing no obvious holy symbol.)

He hates all these possibilities.

"Okay, so, Lady of Loss, what's she up to?"

"When the world was young, she went to some effort to prevent the creation of the sun and moon and all other light sources. She created the Shadow Weave-- and even if I was not personally biased by my relationship with Mystra, I would disapprove of that. 

But on a less mythic level-- her followers can get quite proactive about causing loss in their Lady's Name."

Concerning!

"And Vlaakith?"

"I'll admit, I don't know much about her. Leader of the Githyanki. Presumably the one putting them up to all the raiding."

"What are githyanki? I don't think I've met one before."

"Oh, you have." He nods towards Lae'zel. (Lae'zel is currently watching Shadowheart so, so suspiciously.)

"Huh. It's weird there's only one species I don't recognize, I'd honestly expect less species overlap on a completely different planet. --What's their deal?"

Cayden has a broadminded attitude towards raids. Many times, the people being raided started it. 

"I know less about them than I'd like." Gale sounds like he knows less about all topics than he'd like. "They live in the Astral Plane, raid the Prime Material on occasion, seem to have some sort of deal with red dragons, and hate mind flayers."