  The discovery of supernova SN 1997ff at z~1.7 has confirmed the expected
switch from cosmological acceleration to deceleration, as predicted by the
concordance Lambda/CDM model. However, its position in the SN Ia Hubble diagram
suggestes that the switch is too pronounced, which here is taken to mean that a
cosmological constant is not an adequate description of the state of the
vacuum. An 'oscillessence' model is invoked, with a scalar field phi governed
by a simple quadratic potential, which gives a better fit to the new data
point. The field is undergoing coherent oscillations, and a key feature of the
proposal is that we are towards the end of the second period of acceleration; a
Lambda/phi mix replaces Lambda/CDM, with Omega_Lambda~0.4 and Omega_phi~0.6.
