So the party was sneaking into the manor of Polyphemus Estudian to steal the book he had just finished composing. The theft was commissioned by the Library Lich, who has issues with any books not being in his collection, and apparently hadn't convinced Lord Estudian to sell the book to him.
Having realized that the pictures on the walls in the Entry Hall were all some species of mimic, the group proceeded upstairs. Their sorcerer, Toruv, was ethereal (because of his magic cloak) and thus ghosted through the rooms, discovering a guest bedroom, the master bedroom, a treasury, a hall for fighting practice, and finally a library. The others were searching separately in the physical realm, and found the guest bedroom and -- across from it -- their first locked door. The Arcane Trickster, Barrith, attempted to pick the lock and discovered that at least one of the twin doors to the treasury was a mimic. He managed not to be caught by it, backed out of range, and apologized (quietly).
They proceeded on, finding the training hall and the library. (OOC: At this point, the only room on the second floor that they hadn't entered was the master bedroom, and the sorcerer had ghosted his way through that long enough to realize there were people asleep in there.) They entered the library and began checking the shelves, ignoring the table and chairs in the center of the room. After a while, the arcane trickster came to a single, unadorned book sitting on its own lectern. The book is closed. The swashbuckler, meanwhile, has moved across the hallway to peer into the training hall. The druid is currently a spider, and is riding on the arcane trickster's shoulder.
The sorcerer, meanwhile, has used his ghostly state to drift up through the ceiling and take a look around the attic. The attic is a single, large space. It has a few stray wooden boxes and a couple of wardrobes, but it's mostly empty. He notices something on the south wall/ceiling, and moves to investigate; it's a carved wooden face, much wider than it is tall, stretching across the middle third of the attic. Under the circumstances, he finds this disturbing.
Meanwhile, the trickster picks up the book and opens it to the faceplate, where he reads: "The Mimic Book of Mimics, by Polyphemus Estudian". Clearly, this is the book they're looking for. Even more clearly, they're now in trouble: the book sprouts teeth around its edges and shouts: "HEY! PUT ME BACK!"
The arcane trickster casts Rope Trick as the swashbuckler comes charging back into the room. The swashbuckler swarms up the rope and disappears into the magical space beyond; the trickster follows, carrying the druid with him. This would be a great way to hide, except that the table, the chairs around it, and the rug underneath are all part of a single large mimic, and it's stuck out a tendril and grabbed the rope.
The trickster uses Mage Hand to lower the book back to its lectern, then pulls out his crossbow and threatens to shoot the table if it doesn't quiet down. He gets lucky: the table-and-chairs-mimic is surprised enough that it loosens its grip on the rope long enough for him to yank it loose and haul it up into his spell.
So that's where they are now: three of the four party members are hiding in a spell, with a large, angry mimic underneath them; Lord Estudian is likely to show up any minute; and the fourth party member is on the top floor, unaware of any of this.
As their DM/GM, I'm actually quite proud: the Trickster's player got back to me before nightfall with a full, workable plan for how to get out of the situation. We'll pick up next week as he implements it.