Two miles down the road from the white marble walls of the fabled Taj Mahal, a heavyset man crouches in the dirt of a cow shed and explains how the future of India belongs to him. Digvijay Nath Tiwari is commander of a vigilante group that claims 5,000 members in the northern city of Agra, and which cultivates informants, swarms shop owners, ambushes trucks at night and metes out extra-judicial violence, all for one cause: protecting the holy cow, an animal held sacred by Hindu beliefs. Across the country, hardline Hindu groups have made headlines after being captured on video insulting and beating men they accuse of involvement in cow slaughter. "Retaliation is important at times," said Tiwari, as he sat with 17 men squeezed around a straw mat on the shed floor. His cell phone contained photographs of stick-wielding men rushing to the aid of fallen cattle.

Local police say they cannot stop Tiwari's actions, laying the blame partly on lax laws.

The "gau rakshaks", or cow protectors, are inflaming tensions among India's religions and castes. They risk undermining Prime Minister Narendra Modi's efforts to focus on economic advancement, even as the right-wing Hindu nationalist forces that got him elected promote their own agenda.

The implications reach far beyond the winding alleyways of Agra. Social and religious stability are key to future assumptions of prosperity in India, currently the world's fastest expanding major economy.

"India will remain one of the strongest growth stories in the region," a Goldman Sachs strategist said in April, echoing the sentiment of many foreign investors.

Yet such outlooks built on macro-analysis risk missing a ground truth: if the right-wing groups empowered by Modi's rise do not stop antagonizing minorities, then the ruling Bharatiya Janata Party's (BJP) plans for nurturing that growth will not easily come to pass.

CHANGING FOCUS

Cow slaughter is illegal in most of India, an overwhelmingly Hindu nation. However, it had long been tolerated under the Congress party, which ruled the country for most of its independent history and prides itself on protecting Muslims and lower castes who ply the meat and leather trade.

Now the Hindu nationalist BJP is in power, and that is changing as vigilante groups gain prominence. And Modi, while saying he's concerned, has been either unwilling or unable to halt their more extreme actions.

The prime minister was trained and nurtured by hardline Hindu organisations that were instrumental in his rise from the son of a train station tea seller to leader of the world's biggest democracy.