Fireball clues:
1) Martem's necklace. -> A Necklace of Fireballs produced by a well known magic jeweler, designed to be reliable and pass notice. See
this post and
this one.
2) Zander's observations on the roof. -> It was a nimblewright that threw the fireball stone. Idrassa's contact is going to provide a list of nimblewrights and theorized a way to detect nimblewrights. -> A nimblewright matching the correct description is in Lady Yalah Gralhund's retinue. ->
Lady Yalah's nimblewright threw the fireball.
3) Note and key on the dead gnome (Dalakhar) -> note from Kalain of the Nine Waters -> Kalain provided a stack of Lord ir'Nelview's papers (see
this post).
4) Dalakhar's room contained a death mark from House Tarkanan
Supposition:
A) Declan's encounter with Floxin (he was a tough merc, dressed the same as 3 dead Tarkanan thugs). -> Floxin headed west from Trollskull Alley and was in no condition to travel very far.
B) Renaer's father's stole half million galifars. See this post. -> The Tarkanans who kidnapped Floon seemed to be looking for the money as well as something called the Stone of Golorr. See this post.
House Tarkanan:
There's a low level an escalating street war going on between Daask and House Tarkanan -> "Somebody stole something from someone," per a Tarkanan thug guarding a ritual site and teleportation ring (see this post)
A Tarkanan agent was following the group around the city and taking notes of their activities
House Tarkanan is trying to brainwash broadsheet publishers
A high level spellcaster set up a teleportation circle under a tower in Castle Ward being used by House Tarkanan cultists of the Mockery
Shan Chien the tabloid publisher is going to research Manshoon and bring his results to you in a few days (he also wants to interview you and feature you in his paper)
The Grand Game:
Powerful groups (likely more than just Daask and House Tarkanan) seem to all be looking for Renaer's father's stolen money. See this post.
House Tarkanan kidnapped Renaer ir'Nelview and Floon Blagmaar, looking for information on the Stone of Golorr -> the interrogation was interrupted by a Daask raid on their hideout -> the party rescued Floon (case of mistaken identity, see this post that also mentions their interest in the Stone of Golorr) from a Daask hideout in the sewers (leaving alive a blue goblin and Grum'shar, a half-orc spellcaster) and briefly encountered a mind flayer