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<p>A large array of proxy records suggests that the “4.2&thinsp;ka event” marks an approximately 300-year long period (<span class="inline-formula">∼3.9</span> to 4.2&thinsp;ka) of major climate change across the globe. However, the climatic manifestation of this event, including its onset, duration, and termination, remains less clear in the Indian summer monsoon (ISM) domain. Here, we present new oxygen isotope (<span class="inline-formula"><i>δ</i>¹⁸O</span>) data from a pair of speleothems (ML.1 and ML.2) from Mawmluh Cave, Meghalaya, India, that provide a high-resolution record of ISM variability during a period (<span class="inline-formula">∼3.78</span> and 4.44&thinsp;ka) that fully encompasses the 4.2&thinsp;ka event. The sub-annually to annually resolved ML.1 <span class="inline-formula"><i>δ</i>¹⁸O</span> record is constrained by 18 <span class="inline-formula">²³⁰Th</span> dates with an average dating error of <span class="inline-formula">±13</span> years (<span class="inline-formula">2<i>σ</i></span>) and a resolution of <span class="inline-formula">∼40</span> years, which allows us to characterize the ISM variability with unprecedented detail. The inferred pattern of ISM variability during the period contemporaneous with the 4.2&thinsp;ka event shares broad similarities and key differences with the previous reconstructions of ISM from the Mawmluh Cave and other proxy records from the region. Our data suggest that the ISM intensity, in the context of the length of our record, abruptly decreased at <span class="inline-formula">∼4.0</span>&thinsp;ka (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>∼</mo><mo>±</mo><mn mathvariant="normal">13</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="32pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="629d606b4e9b4d0f5842ae5c0f617885"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cp-14-1869-2018-ie00001.svg" width="32pt" height="10pt" src="cp-14-1869-2018-ie00001.png"/></svg:svg></span></span> years), marking the onset of a multi-centennial period of relatively reduced ISM, which was punctuated by at least two multi-decadal droughts between <span class="inline-formula">∼3.9</span> and 4.0&thinsp;ka. The latter stands out in contrast with some previous proxy reconstructions of the ISM, in which the 4.2&thinsp;ka event has been depicted as a singular multi-centennial drought.</p>