Timeline: Firefly: After the tv series but before Serenity. Primeval: Series 3, after episode 6.

"Captain, what is it?" Zoe asked, turning toward Mal. Floating in front of them was what looked like a roundish ball of light with shards of glass floating around in it.
"I have absolutely no idea. Find Simon and River. Maybe one of them will know.
"I'll find them." Kalee said and then ran down the steps of Serenity toward the medical bay. Jayne reached out his hand but Mal slapped his hand away.
"What are you doing? For all we know, this could be some weird kind of bomb made by the alliance."
"OK, OK. I won't touch it. Relax"
Kalee hurried back up the stairs, closely followed by Simon and River.
"What is that?" Simon was staring at the glowing thing in confusion.
"I was rather hoping you could tell me that. Zoe came down and found it."
Simon shook his head, "I've never seen anything like it."
River was staring at it with a smile on her face. She lifted her hand and ran her finger through the light. Simon tried to stop her but she had already pulled her hand away.
"Simon, it's fine."
Mal looked at her curiously, "Do you know what it is, then?"
River smiled again, "It's a multidimensional tear in the fabric of the multiverse."
Jayne rolled his eyes, "And for those of us who don't speak crazy?"
Now Simon was looking at the thing in awe.
"It's a crack in time." At that moment, a dark shape appeared inside the glowing thing and rapidly started growing. Everyone backed up and Wash almost fell off the edge of the step. Finally the shape revealed what it really was. A group of three people emerged from the glowing thing and a fourth quickly followed. The fourth person, a man dressed all in black lent forward and whispered in the front man's ear.
"We aren't supposed to go through anomalies unless there is an emergency, remember?" The front man ignored him and smiled at Mal and his crew.
"Alright?"