Running 3 players through candlekeep, the means of how they know each other was 2 characters run a private investigation/hired muscle agency and the third hires them to help locate a lost library.

One of the 2 in the agency is a shape-shifter but doesn't want to disclose this to the character that hired the agency.

All level one characters mild encounters until they run into the 4 goblins. PC 1 (cleric) will be the one that hired the agency, Agent 1 (rogue) will be the shape-shifter, and Agent 2 (caster) will be the other member of the agency.

PC 1 moves into tall grass to get concealment from goblins, Agents 1 and 2 follow.

Agent 1 shape-shifts into a hobgoblin in hopes of bluffing the goblins or something.

PC 1 is to the far right of the group and pops up to make ranged weapon attack.

Agent 2 is in the middle of the group and proceeds to move away from Agent 1 (looks like running from the hobgoblin) crossing paths with PC 1 in the process.

Agent 1 makes deception check as action to confuse the goblins, rolls a 20. Total is like 24 with bonus. Goblins freeze in place confused.

PC 1 rolls a 4 on insight to see if they recognize Agent 1. PC 1 is convinced that a hobgoblin is attacking and thats why Agent 2 ran away from them.

Normally, I don't allow pvp but impossible to avoid in this situation, because Agent 1 never disclosed that ability, rolled max on deception, and Agent 2 "fled" from them. PC 1 almost minimum insight check which I allowed a second check after Agent 2 "ran away," because there was no attack of opportunity taken. Second roll was a 2.

PC 1 proceeds to attack his closest enemy, Agent 1. PC 1 rolls a critical on his attack roll and nearly maxed damage rolls dropping Agent 1.

Goblins see PC 1 kill a hobgoblin and all converge on him for attacks. 4 ranged weapon (s. bow) attacks later and PC 1 is down.

Agent 2 runs away to escape back to nearest town.

This sucks. No one likes losing a character, even if it's the first session with a level 1.

I am apologizing to the players and they all stop and tell me to stop and that it was their faults for trying to be mysterious and not communicating.

I still felt bad. So when the next set of characters came through I let then fine and loot the gear of their other characters for extra gold.

Lesson learned was to not try and be so mysterious that you fail to let your allies know what your up to.