  An integrable Heisenberg spin chain with nearest-neighbour couplings,
next-nearest-neighbour couplings and Dzyaloshinski-Moriya interacton is
constructed. The integrability of the model is proven. Based on the Bethe
Ansatz solutions, the ground state and the elementary excitations are studied.
It is shown that the spinon excitation spectrum of the present system possesses
a novel triple arched structure. The method provided in this paper is general
to construct new integrable models with next-nearest-neighbour couplings.
