In this continuation proposal, we propose to study the spin excitations of the spin 1/2 square lattice Heisenberg antiferromagnet CAPCC in fields just below its saturation field. The idea is to test competing theoretical predictions for the behaviour of this generic quantum spin model under intense magnetic fields. One prediction is that spin waves become unstable and decay into higher order excitations in parts of the Brillouin zone. Another is that one should see incommensurate modes akin to those seen in s=1/2 Heisenberg chains when these are subjected to magnetic fields. A very recent experiment on deuterated single crystals proved the feasibility of the proposed experiment but an unexpected magnet quench prevented us from obtaining data of sufficient statistical quality.