Under Anton’s leadership, Wm H. Müller & Co. grows into a highly profitable, international company in ore and shipping. For that reason, in 1900 he decides to move the company’s headquarters to The Hague, where he can develop a lucrative network of politicians and diplomats. He purchases two villas on the waterfront in the Van Stolkpark, on the edge of Scheveningen. The Hague society architect Leo Falkenburg is commissioned to renovate the offices at Lange Voorhout No. 3 and both the residences. One villa is converted into a coach house with stables and staff quarters, while the elegant neoclassical Huize ten Vijver is built on the foundations of the other. There, the Kröllers take up residence.

In 1905 Helene and her daughter start taking art appreciation classes from the art educator H.P. Bremmer. She soon invites him to come and give her private lessons at her home. This becomes a turning point in her life. He introduces her to modern art and opens her eyes to a personal, empathetic experience of art. Under his influence, she begins collecting art – her first acquisition is It comes from afar by Paul Gabriël – and in 1907 she employs Bremmer as her personal advisor to ‘assist [her] in assembling an art collection’.

In 1907, Sam van Deventer joins the hockey club ODIS (Our Goal Is to Score), where he comes into contact with the Kröller family. After graduating, Van Deventer sends Anton a letter inquiring about the possibility of a job at Müller & Co. In Anton’s absence, Helene sends a comprehensive answer about the opportunities at the company. In 1908, Sam is hired as the youngest clerk at the Batavier Line, but the postcard also marks the start of a lifelong, intimate friendship.

Helene had already been collecting antique furniture, ceramics and Asian art for several years. But as of 1907 her focus turns mainly to modern painting. Bremmer is a great admirer of Vincent van Gogh, and under his supervision Helene purchases her first paintings by the then still rather unknown artist in 1908: Edge of a wood and Four sunflowers gone to seed. A year later she acquires The Sower (after Millet) and Basket of lemons and bottle. She writes about this work: ‘If I want to understand Van Gogh’s lemons, I just place a few lemons beside them in my imagination – as I see them, and then I feel the world of difference’.