Occasionally this column will spread a topic over two weeks.

When it happens, it's dictated by the subject, perhaps because of its historical importance, as in our coverage this year of the centenary celebrations of the first performance of Stravinsky's Rite Of Spring.

That was an easy one. This week's topic, whose immense narrative background has a chilling political edge, might be less familiar. But right now, because of a seminal new recording, it has a vital relevance that gives it a sense of blazing immediacy. It revolves around a single piece of music by Dmitri Shostakovich. It's about Shostakovich's least-known symphony, one which the composer himself "disappeared" on the morning of its scheduled first performance in 1936, consigning it to a cupboard for 25 years. It re-surfaced only in 1961, well after the death of the archi-tect of the Great Terror, Joseph Stalin.

The symphony Shostakovich removed so abruptly from the public eye was his Fourth Symphony in C minor. I have written about this symphony before. It is a huge masterpiece. I do not accept the view of apologists who see it as a work of "transition", that shows Shostakovich to have been on his way somewhere but not quite there.

My own view is unequivocal. Not only is this beast of a symphony a masterpiece of staggering ambitiousness, it is, among Shostakovich's 15 symphonies, one of the greatest. It is Shostakovich's greatest undiscovered and misunderstood symphonic masterpiece.

Even today, the Fourth Symphony is not played much in concert. It needs vast resources: it features the biggest orchestra Shostakovich ever used. We've been quite lucky in Scotland. We heard it here in the 1980s from Neeme Jarvi and the RSNO, who then made a benchmark recording of it for Chandos. And we heard it again during Alexander Lazarev's reign with the RSNO in a complete cycle of Shostakovich's symphonies. More recently we heard it when the RCS Symphony Orchestra played it in the Stevenson Hall with Baldur Bronnimann conducting the giant student band in an impressive account. And the UK premiere of the Fourth Symphony was at the Edinburgh International Festival in 1962.

After the spectacular success of his First Symphony and the wild ­extravagances of his Second and Third Symphonies, six years passed without a symphony from Shostakovich. In this period, though he was extremely busy composing, he discovered Mahler.

The influence of Mahler's music, and its one-world view of all human experience, with all of life's vulgarities, trivialities and banalities as well as its loftiest dreams and aspirations, personal terrors and tragedies, seeped into the Russian DNA of Shostakovich, and manifested itself in the Fourth Symphony. Its expression was extreme, from the blatant shrieks of the symphony's opening through to the cataclysmic collisions of consonance and dissonance in the coda of the three-movement symphony an hour later.

Shostakovich was on a hiding to nothing with this piece. He had already been pilloried in Pravda, in an editorial allegedly written by Stalin himself, for producing music that did not conform to the party line. Now, at rehearsals for the new symphony, the musicians were antagonistic, the conductor was uneasy, and the orchestra director warned Shostakovich to withdraw the work before his own hand was forced. The next morning, Shostakovich did just that, putting out a statement that the symph-ony was "incompatible" with his current creative concerns. And that was it. It was gone. Or was it? More next week.