Promotion-chasing Northampton appeared to be cruising to victory when they led 3-1 after goals from leading scorer Scott McGleish (2) and Junior Mendes.
McGleish scored in the 21st and 67th minutes and he also set up Mendes for the third goal in the 77th minute.
But Torquay, outgunned in the first half, levelled first through a Tony Bedeau penalty in the 56th minute.
And, just when all seemed lost, they hit back to draw with a close-range effort from Jo Kuffour in the 82nd minute and a last-gasp diving header by Kevin Hill in the 90th.
There was also controversy over McGleish's second goal, with Torquay players and head coach Leroy Rosenior insisting that they had stopped playing because they heard referee Lee Probert blow his whistle, admittedly for a foul to Northampton, before McGleish scored.
Mr Probert waved play on and gave the goal.
Northampton should really have wrapped the game up long before the end.
They dominated the first half, but had only McGleish's sweet left-foot volley to show for it. McGleish could have had a hat-trick before the interval on his own.
Injury-hit Torquay levelled for the first time with Bedeau's spot-kick, after Jason Crowe had fouled Hill.
McGleish's second goal seemed to knock the stuffing out of Torquay, especially when McGleish set up Mendes for number three with a clever backheel pass.
McGleish also hit the post, but then Kuffour forced Paul Robinson's cross over the line to give Torquay hope in the last ten minutes.
And as the match moved into stoppage time, substitute Craig Taylor nodded a James Sharp free-kick across the goalmouth and Hill threw himself in to head the equaliser.