  Given a generic family $Q$ of 2-dimensional quadrics over a smooth
3-dimensional base $Y$ we consider the relative Fano scheme $M$ of lines of it.
The scheme $M$ has a structure of a generically conic bundle $M \to X$ over a
double covering $X \to Y$ ramified in the degeneration locus of $Q \to Y$. The
double covering $X \to Y$ is singular in a finite number of points
(corresponding to the points $y \in Y$ such that the quadric $Q_y$ degenerates
to a union of two planes), the fibers of $M$ over such points are unions of two
planes intersecting in a point. The main result of the paper is a construction
of a semiorthogonal decomposition for the derived category of coherent sheaves
on $M$. This decomposition has three components, the first is the derived
category of a small resolution $X^+$ of singularities of the double covering $X
\to Y$, the second is a twisted resolution of singularities of $X$ (given by
the sheaf of even parts of Clifford algebras on $Y$), and the third is
generated by a completely orthogonal exceptional collection.
