Heavy hadrons interacting via pion exchange can form bound states (hadronic molecules), analogous to conventional nuclei. The potential between charmed hyperons and charmed mesons, with parameters constrained by the deuteron, leads naturally to a bound state, whose mass and quantum numbers are consistent with the LHCb "pentaquark" Pc(4450). An appealing feature of the model is that it does not imply a proliferation of unobserved partner states. Within a significant (and constrained) parameter range, and independently of the poorly-known short-distance potential, only one additional partner with the same flavour is expected, and its experimental absence (so far) has a possible explanation. A further partner with different flavour is also predicted, and could be discovered in Lambda_b decays. A characteristic feature of the molecular interpretation is isospin mixing, resulting in striking signatures in production and decay.