Damros walks slowly down the lane with Xaul - several paces behind Skye and Sehaethas.  "At least it seems to be a paying job.  We can only hope it is not another 'clean up the sewers' mission.  I still haven't gotten the stink out from the previous visit below the city streets."    He keeps a casual scan of the lane as they head back to 'home base'.

Passive Perception:  14

Skye answers "We are to stop a murderer in the Dock Ward. If we can kill him, we get more money. Break the law, get paid more. Risk and reward and all that. It shouldn't be the sewers. He only strikes at night. Do we want to see if we can find him tonight or do you all wish to sleep and try tomorrow?" 

Kylaski takes, changing Sehaethas into a female Tiefling again. Chi says, "Let's take a look tonight!" Her tail twitches with eagerness...

Xaul agrees with Kylaski, 'Yes, tonight sounds good, get it over and done with. Do you have a plan in mind?'

(I have seen a few plans in the OOC, is there an agreed option or do you wish to plan in character?)

Skye spits to one side as they discuss it.

Either they have one of them disguise themselves as an elf/half-elf, able to play along with the villain-soon-to-be-victim as needs be. 

Or, they cast a silent image of a longer dock with a sleeping victim upon it, over water with Xaul ready to pounce upon whoever falls in, and the rest of of them ready to push the killer into the water if they don’t step upon the illusionary planks. 

Skye votes for the latter of the two options. With Xaul able to fight as usual, and her able to jump in and support, the plan seems to use their advantages over an enemy who is unlikely able to be able to tolerate the underwater combat. 

Xaul also agrees that he'd prefer the latter, especially since it involves getting into the water from the get go. 'Been weeks since I've been able to submerge myself in some good and proper brine!'

Kylaski agrees with, "That sounds fun."

Chi then speaks in Sehaethas' voice, "It's more likely to be a long boring wait with nothing happening. Also, shouldn't we change out of these fancy clothes first?"

"A wise point, Sehaethas.  I suppose I need to grab some shabby bits to help 'the look'..."   Damros gave a tight lipped grin.  "It has been a long time since I have been 'bait'."

“I could use a spear, or anything that’s good for poking them as find themselves underwater. Any suggestions?” Skye says, directing the latter part toward Xaul. Though she can hold her breath forever, she can’t speak spell invocations under water, and she’ll need something to attack with if she followers the killer into the drink. 

"Think we might find a boat gaff down near the docks? It is something typically found around boats... and would NOT be be seen as 'out of place' like a spear or trident?"    Or maybe even just a stout pole with a sharpened end?" 

Damros goes on and on about improvised weapons... which runs out of steam after a couple minutes.

It's possible to find an improvised weapon if you wish that is spear or trident like enough for underwater combat.

I will need a stealth check from everyone staying on land. 

Damros   Stealth Check:  21    {game log}

(If we are going with plan silent image, Skye will find an improvised spear, then go into the water holding her breath, then cast silent image from 60 feet away, popping her head up to recast as necessary. Give Xaul some underwater company). 

(( I am assuming Damros got such a great STEALTH result (not just from the die roll) due to the typical large waterport docks... plenty of ships docked; plenty of crates stacked for loading or being unloaded;  large coils of ropes near dock piling posts.    Lots of 'things' to skulk behind and duck in and out of their shadows. ))

Just need a stealth check from Sehaethas unless plan B is happening simultaneously with plan A

Only an 11 for Sehaethas on Stealth.

After an hour of waiting, you (if on land) see a drunken half elf stagger out of a nearby tavern, drunk. He starts to be followed by a cloaked figure with a scimitar. He looks around to make sure no one is watching, and spots an easier target at the docks, just far enough to be hidden from prying eyes, and with the ability to dispose of the body too. He moves towards the illusion. and as his foot goes through the first plank, he realises he has been tricked. But it is too late! (I rolled a dex save, DC12, and got a nat 1). He falls into the water, and we are in initiative. He is surprised so gets disadvantage, which even with a high modifier just puts him after you.

Everyone is up! He is underwater currently. The water has moved the cloak revealing that he is a drow! (and can't seem to breathe underwater. That would have really ruined your plan)

As the drow plunges into the water, his cloak snagging in the current and around his flailing form, Skye moves to swim above him, barring his way to the air above.

She stabs out at him with her spear (Attack: 16. Damage: 2 ), trying to drive him deeper down into the bay. 

Xaul, who was lurking just 5 feet beneath the surface as planned, immediately acts when he feels and hears that the water is disturbed with a crash, his orcish form bursting up and out of the water with a spray, done with the grace and agility of a dolphin, for just a split second so he can quickly cry the verbal component to eldritch blast. The ghostly green, fist shaped beam tears through the water and into the target before he can even sink back down again, splitting the ripples with crackles of power. As Xaul once again assumes his preferred position beneath the waves, he also unscrews his bottle lid and lets his patron loose, commanding the undulating and fierce surface of the water into a single rising wave, with the tentacle then crashing down but missing its target. [Action: 15 + 4 = 19 to hit with Eldritch Blast, 8 force damage on a hit, Bonus Action: 5 + 4 = 9 to hit with Tentacles of The Deep, 6 cold damage on a hit]