A substitution network is a wireless solution whose purpose is to bring back connectivity or to provide additional bandwidth capac- ity to a network that just suffered a failure or a dramatic surge in its workload. We analyze the performance of the simplest possible multihop topology for a substitution network, i.e., the multihop chain subject to traffic transmitted in both directions. Clearly, the potential capacity of a substitution network, whose technology should be embedded in mobile routers, is very likely to be far much smaller than the prior base network. We investigate the actual performance attained by such a substitution network under various conditions of the chain length and the carrier sensing range. Our results show that the capacity, viz. its maximum at- tainable throughput, reaches a peak at a given workload and then, for larger values of workload, decreases towards an asymptote which value can be drastically lower than the peak value. We give insights into this performance collapse and show the need for a suitable admission control.