In Chap­ter 25, titled “The Art Thief,” the pro­tag­o­nist’s urge to steal art inten­si­fies, lead­ing him to a series of sig­nif­i­cant heists. Ini­tial­ly, he dis­guis­es his activ­i­ties, steal­ing a sil­ver sug­ar bowl, two Com­mu­nion chal­ices, a stained-glass win­dow­pane, a soup tureen, and a com­mem­o­ra­tive medal­lion, while deceiv­ing Anne-Cather­ine about his crimes in Switzer­land. He breaks his per­son­al best by snatch­ing ten items in one day from a muse­um, includ­ing a teapot and sev­er­al sil­ver cups.

Return­ing to Gruyères Cas­tle, a mem­o­rable spot from his past with Anne-Cather­ine, he decides to take on a mas­sive tapes­try that had cap­ti­vat­ed him ear­li­er. Despite her reluc­tance to risk impris­on­ment for art theft, he feels empow­ered to act alone, wrap­ping an emp­ty duf­fel bag around his leg to aid in the theft. After detach­ing the tapes­try, he strug­gles to con­ceal it but even­tu­al­ly hoists it out a win­dow and retrieves it from the mud­dy ground out­side, cel­e­brat­ing his dar­ing achieve­ment.

His crim­i­nal exploits con­tin­ue as he devis­es a plan to steal a stat­ue of the Vir­gin Mary from Saint Sebas­t­ian Chapel. While Anne-Cather­ine is at work, he uses her spa­cious car to trans­port the 150-pound carv­ing after suc­cess­ful­ly unbolt­ing it. Although thrilled, he faces her dis­ap­proval as the scent of incense lingers in her car, and she resents his unau­tho­rized use of it.

As his col­lec­tion grows, the once-prized art begins to suf­fer from neglect. He crams the tapes­try from Gruyères under the bed and endan­gers the integri­ty of the apothe­cary paint­ing, which starts to warp due to being stuffed away care­less­ly. Breitwieser’s attempts to restore these pieces him­self result in a dev­as­tat­ing loss when a ceram­ic plat­ter and a small still-life paint­ing shat­ter.

Anne-Cather­ine feels lost in the chaos, rec­og­niz­ing that his steal­ing has turned into a com­pul­sive and destruc­tive behav­ior, con­trast­ing sharply with his ear­li­er appre­ci­a­tion for beau­ty. Yet, despite this decline and her grow­ing dis­sat­is­fac­tion with his trea­sures, she does­n’t leave him. Their rela­tion­ship endures as both turn thir­ty, but the attic, once a repos­i­to­ry for their love of art, has trans­formed into a clut­tered tomb of dis­card­ed aspi­ra­tions.