Crooked, devious, oblique mean not straight or straightforward.
Crooked may imply the presence of material curves, turns, or bends. In its frequent extended use it applies especially to practices (as fraud, cheating, or graft) involving marked departures from rectitude.
Devious implies departure from a direct, appointed, regular, or fixed course and hence suggests wandering or errancy and, often, circuitousness.
The term as applied to persons and their acts or practices usually implies unreliability and often trickiness or shiftiness.
Oblique implies a departure from the perpendicular or horizontal direction, or a slanting course and in extended use suggests indirection or lack of perfect straightforwardness.