The other is an original script titled The Serpent, and comes from Ripper Street’s Richard Warlow.
The Three follows a mystery that begins after three children miraculously survive four plane crashes, with a fourth child rumoured to have lived.
Peter Straughan (Wolf Hall) is adapting the series, which is billed as a “multi-stranded international thriller with a supernatural twist”.
The Forge is producing the 8x60mins series, with Kate Sinclair, George Faber and Elizabeth Kilgarriff executive producing.
The Serpent also runs to eight hours, but is based on the true story of Charles Sobhraj, who was the elusive chief suspect in the murders of up to 20 young Western travellers in Asia in the mid-1970s.
Poldark producer Mammoth Screen is attached to produce, with director Tom Shankland executive producing alongside writer Warlow, Preethy Mavahalli, Damien Timmer and Kilgarriff.
“It’s my ambition to deliver original, bold and unexpected drama to BBC One, drama that is set apart from what is on offer elsewhere and which allows us to explore new worlds,” said BBC controller of drama Piers Wenger. “These two new series do just that, each offering a big emotional story in an international setting with iconic characters at their heart.”