Genuine crossovers, where characters from both universe's meet and hold their own in balance with each other, are remarkably hard to write particularly when, as here, you are throwing a genuine plot into the mix. The Tenth Doctor meets the Firefly clue, facilitated by River Tam.

The Man With No Name (95869 words) by Frostfyre7
Chapters: 31/31
Fandom: Doctor Who (2005), Firefly, Serenity (2005)
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Characters: Tenth Doctor, The Doctor (Doctor Who), Malcolm Reynolds, Inara Serra, River Tam, Zoë Washburne, Simon Tam, Jayne Cobb, The Doctor's TARDIS, Serenity Crew, Serenity (Firefly)
Additional Tags: Crossover
Summary:

He hadn't really counted on getting into a pub brawl over the color of his coat on some speck of a planet, or signing up with a crew of petty criminals. Still, he'd always wondered what really happened to those Lost Colonists from Earth...