This proposal is part of our research programme on novel quantum phases in frustrated lattices. Here we propose to determine the magnetic structure in a quasi-two-dimensional organic material where magnetically-active dimers carrying spin-1/2 are arranged in a triangular geometry. Organic materials have extreme tunability and realize a very rich variety of correlated electron phases (superconducting, spin- and charge-density wave, spin liquid), much studied theoretically, however microscopic experimental studies have been missing due to difficulties in sample synthesis. We have recently obtained 1mm^3 crystals of one family of organic materials expected to show commensurate antiferromagnetism and propose to use WISH to determine the magnetic structure. If successful, this will be the very first determination of the magnetic structure in the parent family of organic superconductors.