  Legendre curves play a very important and special role in geometry and
topology of almost contact manifolds.There are certain results known for
Legendre curves in 3-dimensional normal almost contact manifolds. The aim of
this paper is to study Legendre curves of three-dimensional $C_{12}$-manifolds
which are non-normal almost contact manifolds and classifying all biharmonic
Legendre curves in these manifolds.
