By April 1942, Klein was composing once again, and was busier than ever. He had a steady stream of new compositions, was preparing for, and performing in, concerts and rehearsals, and had his general responsibilities in the Free Time Administration. In addition, he was involved in the Youth Care Department, and was taking part in an ambitious lecture series. The main office of the Free Time Administration was in the Magdeburg Barracks (now part of the Terezín Memorial Museum and its archives) and so, in addition to his other workplace, L417, the Magdeburg is where he spent much of his time. Irma Semecká worked in the office and, in the final months of his imprisonment, they became very close, eventually falling deeply in love. Klein's senior by three years, she was enormously intelligent in her own right. She confided, in a letter to Lisa dated 3 June 1945, that ‘in those six months we did not say a single bad word to each other’. He used to visit the office ‘to warm up when his fingers were nearly freezing to the keys of the piano’, Irma recalled:

The studio, as Klein proudly called it, was in reality ‘a dark squalid cubbyhole with a window and bars, an old mattress replacing the window glass’, Irma said. She continues:

Klein's fellow pianist and friend from Prague, Truda Solarová, has presented a vivid picture of some of his work: