Mission Timeframe: Stardate 239510.01 - 239512.03
What should have been a routine survey of a tide locked planet, turned out to be much more. When the Constitution arrived at the planet they find it to be a desert planet but first scans discover strange readings. They weren't Starfleet if they didn't try to investigate and send away teams down. Shortly after they arrive the Officers get into a sand storm but follow the strange readings that are strong enough to still be readable through that storm.
Once reaching caves that seem to be safe from a storm, they discover the source of the strange signal: A portal. But they have no choice in if they want to step through it. The moment they get closer enough they are simply sucked in and lose consciousness. Once they wake up again they find themselves on Earth, in the 20th Century in a town called Salem. All around them are people in costumes, pumpkins, scary lights and decorations; it's Halloween. The good news, they are believed to be in costumes. The bad news, they discover an ancient alien tech and a shuttle crew from 2345 stranded in Salem as well.
Not only do they have to find a way to return to their own time and place, but see themselves obligated to return the other crew home as well, but those are happy where they are. It takes them a lot of time to find out how to return home, wandering through Salem and trying to navigate the strange environment they discover an area in Salem on a cemetery that shows strange readings and discover that every now and then the Alien tech that brought them to Salem has an 'exit' that pops up every now and then. They make it just in time to return to their own time and once arriving they check the database, seeing that the other crew also had made the decision to return to their own time.