When Enjolras and Bahorel return from a sparring session to room 89, it's with the idea of the loan of a book, and drinks, and doubtless conversation. It turns out, however, that Joly and Combeferre are already in the room.
This is fine, of course; it's no trouble whatsoever. And the rooms are as much Combeferre's as Enjolras's. It's only that Combeferre and Joly are elbows-deep in some kind of experimentation which distracts a certain amount of attention.
There are weird devices that beep and blink with multicolored lights. There are wires and whirring noises. There's a green liquid that's steaming somewhat ominously, although Joly catches Enjolras's glance and assures them both in a bright voice that it's perfectly safe. (Bahorel looks faintly disappointed to hear it.) There's Combeferre's pterosaur specimen, decanted from its jar and hooked up to one of the weird devices, which is producing a warbling wail like a drunken songbird.
It's not worth asking about the experiment just yet, let alone inquiring what world and time those mechanisms might have come from. Enjolras leaves Bahorel to ask anyway, and poke at things, and generally make a nuisance of himself. He himself goes to wash up.
A few minutes later, in shirtsleeves with a freshly washed face and hands, he returns to the main room. He's just in time to see a fountain of brightly colored steam shoot for the ceiling. The little devices are shrieking and warbling, and Joly makes a startled sound -- Enjolras has covered the distance to the table, he's reaching to pull them away, whoever's nearest, out of danger -- but just as his hand closes on Combeferre's sleeve, either his vision wobbles or the air itself does, and they're somewhere else.
Quiet falls like a weight. The table with its devices and bubbling liquid and pickled pterosaur is still there, but the devices have gone silent. Joly is here, Bahorel, Combeferre; his arm is solid under Enjolras's hand.
But under their feet is lush greenery. Strange plants surround them, and a blue sky overhead. The air is warm and swampy and full of unfamiliar odors. There are buzzing noises, and a clattering of strange insects, and somewhere far off a bleat deeper than any sheep or goat. No walls. No buildings; no civilization; no humans in sight, except their little cluster. Nothing familiar at all.
For a heartbeat, they're all wide-eyed.
Then Bahorel is shouting with laughter, and Joly exclaiming and Combeferre starting to sputter questions.
Suddenly there's a loud buzz, and a large dark shape falls from the sky in a rapid, erratic path. Enjolras pushes forward on instinct, putting himself in front of Combeferre, sees Bahorel doing the same--
And they're back in his familiar room at Milliways, just as they were, except that there's a beetle the size of a small dog on the table, tucking its wings away.
(It's only later that any of them will realize just how many days passed in the course of those few moments. This is why you shouldn't play with pterosaur corpses and time-manipulation devices you don't fully understand, kids!)