Z-Spec spectrum of H1429-0028 with observed frequency on the x-axis and flux density (mJy) on the y-axis. Reliably detected lines include CO (J:4 → 3) and CO (J:5 → 4) at z = 1.026 ± 0.002. The channel where CO (J:5 → 4) from the background source is observed is likely contaminated by CO (J:3 → 2) from the foreground source. Colours represent channels with line emission from the foreground source (yellow), background source (red), or a mix from both (blue, see text for more details). The solid line shows the fit to the continuum, while the dashed line represents the 1σ error above the continuum.