The original six-track duo album, Undercurrent, ranked high among the output of both partners. Its pervading pensive ballad mood was only contrasted by a transcendent up-tempo ‘My Funny Valentine’, the highlight of which is 64 bars of Evans’s right hand alone backed by Hall playing rhythm-guitar! This absorbing session was augmented a quarter-century later with the expanded stereo reissue, which added a couple of new tunes and two alternate takes including a fascinatingly explorative ‘Funny Valentine’ at only 80 per cent of the previously known tempo. As to the present reissue, its bonus material consists of the contemporary quintet album, Interplay, adding mostly muted Hubbard plus rhythm-section, along with four originally unissued tracks (all Evans compositions) where Sims replaced Hubbard. As to why anyone would need two different mixes of a mere duo... It would have been far better to replace the mono version with their second and last joint effort, Intermodulation. Apart from the 30-minute stereo/mono duplication, the music stands up extremely well.