NEW DELHI — Returning from a lecture in southern India a few weeks ago, Prof. Anand Teltumbde was booking a cab outside Mumbai’s airport after midnight when security officers approached him in the dark and took him away.

Mr. Teltumbde, a prominent scholar and writer on Indian social issues, was locked in an iron-grilled cell in the nearby city of Pune. For eight hours, he sat behind bars on a dirty mat until a court intervened, ruling that the arrest was illegal.

But it was not entirely a surprise. Last year, the police in Maharashtra, one of India’s largest states, said they had uncovered a vast conspiracy to topple the Indian government that involved Mr. Teltumbde and other well-known writers, academics and lawyers.

Officers raided more than a dozen of their homes, confiscating hard drives and documents. Citing a broad antiterrorism law, the police have put nine of them in jail, accusing them of helping Maoist insurgents, trying to procure grenade launchers, inciting a riot and plotting to assassinate Prime Minister Narendra Modi.