Secrets of Sulphur Springs, on Disney Channel
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Caution: spoilers!

Season one
A 12-year-old boy named Griffin Campbell moves with his parents, Ben and Sarah, and his younger twin brother and sister Wyatt and Zoey, from Chicago to the town of Sulphur Springs, Louisiana. Ben has bought a run-down old hotel called the Tremont, where he used to stay summers when he was a kid. Now he wants to fix the place up and reopen it. Meanwhile, on his first day of school, Griffin befriends a girl named Harper Dunn. He learns about rumors that the Tremont is haunted by the ghost of a girl named Savannah Dillon, who had been a camper at Camp Tremont, not far from the Tremont Hotel, thirty years ago (in 1990), and who had mysteriously disappeared. Zoey and Wyatt explore the hotel trying to find evidence of Savannah's ghost. Meanwhile, Harper and Griffin discover an underground bunker that's accessible through the basement of the Tremont. And the bunker has a hatch leading to the surface, which transports them to 1990. They befriend Savannah, as well as young Ben, and Harper's mom, Jess. Calling themselves "Harry and Hermione", Griffin and Harper try to learn how Savannah disappeared (or died), and prevent it. They keep going back and forth between 1990 and 2020, but this gets more difficult because in the present, Jess doesn't want Harper hanging out with Griffin, so she often has to sneak away to the Tremont. Jess also doesn't want either Harper or her younger brother Topher going anywhere near the Tremont, saying that bad things happen there.

Well, Harper and Griffin eventually discover that Savannah had used the hatch to travel back 30 years herself, to 1960. I don't want to say any more about Savannah right now, but I will say that even in her own time there had been stories about the Tremont being haunted. So I wondered at first if Savannah had died in 1960 instead of 1990, but... it seems there's always been a different ghost at the hotel. I also want to mention that Harper and Griffin discover a way to set the hatch's destination to different years. And in the season finale, Harper goes back in time to try and save her father, who had died in an accident when she was four years old. And there's another trip back even further in time, which sets up a new storyline for the next season.

Season two
Well, first I suppose I should say that last season, Savannah eventually settled in the 1960s, when she was adopted by a woman named Caroline, who worked at the Tremont Hotel in that era. But she occasionally either leaves messages for Griffin and Harper (whose real names she now knows) to find in 2020, or visits them in person. At the end of the season, the three of them visited 1930, after Savannah found a picture of a girl from that time who looked exactly like Harper. This season they learn that the girl was Daisy Tremont, who would become Harper's great grandmother. The Tremont wasn't yet a hotel, but a house on a farm where Daisy lived with her father, Elijah, and younger brother, Sam. Her mother, Grace, was dead, and the kids soon realize she's the ghost that haunts the hotel in the present. At one point, Harper and Daisy switch places, with Harper pretending to be Daisy in 1930, and Daisy pretending to be Harper in 2020. But the crystal that powers the time portal goes missing, so they're stuck in those years. Meanwhile, in the 1960s, Savannah meets a handyman named Sam who works at the Tremont, who is Daisy's brother as an adult. She learns that he's the one who built the time machine, though so far he hasn't gotten it to work. Eventually Griffin recovers the crystal, but it's cracked. Still, Harper and Daisy manage to switch back to their own times. But not before Harper learned that a judge who bought the Tremont farm tricked Elijah and had his family evicted. And she found proof of this trick, which she brings back to 2020 and shows to her mother and the Campbells, who decide to go into business together, with Jess opening a restaurant in the hotel. Now that there are descendants of the Tremonts sharing the property, Grace's ghost departs, and the problems she'd been causing in the hotel finally stop. Three weeks later, the hotel is finally ready to open for business. However, a new ghost has apparently moved into room 205, and causes new problems.

Season three
So, a bunch of stuff happens this season, with a ghost in 2020, and more trouble in 2024. I don't want to go into details about all that, but I will say all the problems are solved by the end of the season, and Griffin and Harper decide to destroy the time machine. But then someone uses the portal, and a kid named Nick comes through and tells them it would be a bad idea to destroy it. I won't spoil who Nick is, but this seems like a hook for another season. I don't know if there'll be another or not, but I kind of hope there will.