Oasis — T.W. Hard

Somewhere in the wastes of the Sudan, Diana Jacobson had vanished. Was it a case of kidnapping, rape or even death? All her brothers had to go on were two clues: a description of the hooded riders with their burning eyes and merciless swords and a strangely carved sapphire as deadly as it was precious.
Unused to peril, James and Jon Paul Jacobson set off into its uttermost heart entering a country where every nomad was an enemy and where even the wind brought death, Strangers to violence, they learned to kill or be killed in a hundred battles.. Afraid of love, they found it on an impossible quest for the woman they had sworn to rescue...or avenge.