Party consists of 2 monks, a bard and a rogue/warlock. We were playing the Sunken Citadel from Forgotten Realms. The mission was to rescue the grandchildren of a rich merchant. The story also involved an apple tree that produces one poison apple and one healing apple a year. The nearby town would purchase both apples from the goblins, but this year the goblins stole it back. We fought our way through the citadel, along the way, freeing a young dragon and discovering that a Druid was responsible for the goblins stealing back the apple. We reached a point where we could see the tree. A group of goblins attacked us, but were quickly routed. A surrender and disarmament somehow turned into wholesale slaughter when I momentarily lost attention to the game(Rogue/Warlocks doing). We were in an opening surrounded by piles of twigs. A Perception check had us noticing that there was movement among the piles so the Rogue/Warlock starts using Prestidigitation to set them on fire. The fire quickly gets out of hand and we are forced to retreat to another room and wait for the fire to die out. The area was still thick with smoke when we reentered the room and discovered 3 bodies at the base of the apple tree. Yep. The Druid, one of the grandchildren and a Paladin who accompanied them had died of smoke inhalation. Oops. We inadvertantly killed our mission. We returned the body to the merchant leaving out the details of how she died. Out of character, our DM revealed to us that the second grandchild had died a month prior and the Paladin and Grand Daughter had been brainwashed by the Druid and were now dependent on the tree to sustain their life. The only way to free them from the evil influence would have been to destroy the tree, but that would have resulted in them dieing within 24 hours anyway. The moral of the story is…even non attack cantrips can be lethal. Who knew?