There were quite a number of proposals over the years involving lines from the Buckingham area to connect with both the NBJR and the EWJR.
This one looks like an abandonment of the 1888 Act 52&53 Vict c.cci (1889) which consisted of five sections of railway:
1) From the Aylesbury & Buckingham Ry to Radclive
2) from an end on junction with line (1) to Towcester
3) from a junction with line (1) to a junction with the LNWR Banbury line at Radclive
4) from a junction with line (2) in Towcester to a junction with the authorised Stratford upon Avon Towcester & Midland Junction Ry at Easton Neston
5) from a junction with line (2) terminating at the NBJR in Towcester
The references to "Towcester" etc refer to parishes, so without the benefit of a map this is all a bit difficult to plot exactly, but it gives an idea of where the lines would have run
Best thing would be to go to Northampton Record Office at Wootton Hall where the Parliamentary Deposited Plans are kept - this one is listed as their ref. no. 199 - it should have a full map/plan with it and will reveal all !