A chiral molecule does not need to have a chiral centre (in the sense of a single atom bound to 4 different groups); sometimes a larger structural feature of the molecule is responsible, with no individual chiral atom. Consider for example a substituted allene
(I hope you are aware that the two =CRR groups are perpendicular to each other, not coplanar as in an alkene.) This molecule has no plane of symmetry, and is not superimposable on its mirror image.
Now consider your molecule. If the two rings were coplanar, the molecule would have a plane of symmetry (neglecting the lone pairs on the amino groups; we assume free rotation about the C-N bonds, and the Ns can invert). But the steric hindrance between the ortho Cl and NH2 groups prevents the rings from being coplanar. What effect does that have?
To say that all "asymmetrical" molecules are chiral is too vague; what is meant by "asymmetrical"? Is this molecule "clearly" asymmetrical?
The most general definition is that a molecule is achiral if it has an improper rotation (rotation-reflection) axis Sn. (S1 is the same as a mirror plane; S2 is the same as a centre of inversion.)