  We propose a system of four quantum dots designed to study the competition
between three types of interactions: Heisenberg, Kondo and Ising. We find a
rich phase diagram containing two sharp features: a quantum phase transition
(QPT) between charge-ordered and charge-liquid phases, and a dramatic resonance
in the charge liquid visible in the conductance. The QPT is of the
Kosterlitz-Thouless type with a discontinuous jump in the conductance at the
transition. We connect the resonance phenomenon with the degeneracy of three
levels in the isolated quadruple dot and argue that this leads to a Kondo-like
dynamical enhancement of symmetry from U(1) x Z_2 to U(1) x U(1).
