The characters are traveling through a valley on the way to their destination when a raging storm drives them to find shelter in a nearby cave.
The cave is dry and clean and about 60 feet in is a large rock to the left. Behind the rock is a cache of valuables (paintings, busts, jewels, etc [worth 230 gold], a stockpile of weapons [swords, maces, shields, spears, crossbows], and 4 weeks rations of food and water for 4 people.
The cave is 200 feet deep and is about 15 feet wide at the opening and 40 feet wide at the back. Their is a magical glyph on the far back wall, painted in white chalk.
Succeeding on a DC 15 Intelligence (Arcana) check, a character recognizes it as conjuration magic, but find it's symbology to be slightly alien.
The storm lasts for 9 hours.
After 2 to 3 hours, the portal at the far wall opens and three Thri-Keen step through in a great rush, the portal closes after 12 seconds.
Jubal (Male, reddish brown carapace, left antenna is broken, stands 5'6" tall). He is the first through and he shouts to his two comrades to warn them of the intruders. He has the Magic Initiate feat and speaks Thri-Keen, Draconic, Elven, Undercommon.
Ista (Female, dark blue carapace, she is wearing a metal lens over her right eye, stands 6'2" tall). She is wielding 2 longswords that she uses in place of her claws. Her lens is a magic item that allows her to add twice her Dexterity modifier to Initiative checks. She has advantage on Charisma (Intimidation) and (Persuasion) checks and the Inspiring Leader feat. She speaks Thri-Keen, Common, and Dwarven.
Malia (Female, yellow-green carapace, missing her secondary right hand, she seems distraught and keeps saying "Ega" over and over, stands 6'5" tall). She wields a great axe and has the Savage Attacker feat. She only speaks Thri-Keen.
Ista demands to know if Gog Zuker sent them. She says that the bounty on their heads isn't worth dying over and warns them to retreat from the cave at once.
If the characters remain calm and communicate, they learn that the group of Thri-Keen are rebels on their world (an alternate Prime they call Teara) and are fighting against the corrupt rule of the Gogs, hobgoblins who control a series of authoritarian City-States. They acquired a magic chalk that allows them to create portals to this cave and use it to steal weapons and valuables to aid their rebellion. They were in a tough fight before escaping and lost one of their band, a thri-keen named Ega and Malia's mate. They are not willing to share their cache or give up the cave under any circumstances, but will allow the characters to wait out the storm before leaving.
If a cleric or a paladin is in the party, and is part of the communications they will learn from Jubal that the gods were killed by the Gogs two millenia ago. Jubal is very curious about their religion and will take notes on what he learns.
If there is a warlock in the party, and is part of the communications they will learn from Jubal that the Gogs are warlocks who serve a fiendish patron named Thur Zomm.
If a fight occurs, and things are looking badly for the thri-keen, they will retreat with the chalk (it's an action for Jubal to open the portal) and the portal will remain open for 2 rounds.