  The quasi-two-dimensional Heisenberg spin $S=1/2$ dimer system
bis(2-amino-5-fluoro-pyridinium) tetrachlorocuprate(II) is studied by means of
inelastic neutron scattering, calorimetry and nuclear magnetic resonance (NMR)
experiments. In the absence of an applied magnetic field we find dispersive
triplet excitations with a spin gap of $\Delta=1.112(15)$ meV and a bandwidth
of $0.715(15)$ meV within the layers and $0.116(15)$ meV between the layers,
respectively. In an applied magnetic field of $\mu_0H_c\approx 8.5$ T the spin
gap is closed and we find a field induced antiferromagnetically ordered phase.
