Mr Haglund's letter talks about his former business partner, W. Jack Richards, who at the time was unwell and was leaving to go to the "the other coast" - he did not return.
The letter ends: "Whoever finds this note will be pulling this construction down ... I hope they do a better job than I have done - cheers + kind regards."
Builder Russell Hall, who is refitting the Queen St store, came across the time capsule as he was working last week. "I was just clearing a bit of rubbish out of the back and it was tucked behind a skirting board."
Mr Hall said he tore into it, saw it it was from 1987, and wondered if he should put it back for the next 100 years.
Instead, he called Wairarapa Times-Age, and we tracked down Heaton Haglund.
Mr Haglund has no recollection of writing the letter, joking that he must have been drunk or on medication, but thinks he probably put it there for a bit of fun. "It's like looking at a distant scene through a mist."
He ran a chemist's shop in the building for about 13 years before setting up The Chemists with others a few doors down, retiring from there two years ago.
Mr Haglund said he does not consider himself a history buff, but is proud of The Chemists' history, which has traded continuously since the 1890s.
Of the 1987 market crash, he said he was fortunate enough to sell a large chunk of shares immediately before it happened.