  We construct an effective Quantum Field Theory for the wrapping effects in
1+1 dimensional models of factorised scattering. The recently developed
graph-theoretical approach to TBA gives the perturbative desctiption of this
QFT. For the sake of simplicity we limit ourselves to scattering matrices for a
single neutral particle and no bound state poles, such as the sinh-Gordon one.
On the other hand, in view of applications to AdS/CFT, we do not assume that
the scattering matrix is of difference type. The effective QFT involves both
bosonic and fermionic fields and possesses a symmetry which makes it one-loop
exact. The corresponding path integral localises to a critical point determined
by the TBA equation.
