In November the US Drug Enforcement Administration issued its Drug Threat Assessment. Mexican ‘transnational criminal organisations’, it said, are the primary suppliers of heroin, cocaine, methamphetamine, and marijuana to the United States. Drugs – the DEA says – are killing 46,000 Americans a year. But between Mexico’s criminal enterprises, and their clients, is a vast expanse of difficult geography and an international border. So, how do cartels get drugs into the US? The Inquiry hears from serving US law enforcement personnel tasked with intercepting drugs shipments. Their stories – of tunnels, “narco-subs” and complex criminal networks – are astonishing.(Photo: Narco-Submarines, Credit: Reuters)

We first asked this question over a year ago. So far, the answer has been no. The attacks in Paris killed 129 people. The day before that 43 people died when suicide bombers hit Beirut. Nearly two weeks before that a Russian passenger jet exploded over Egypt, killing all 224 people on board. The group calling itself Islamic State has claimed responsibility for all these attacks. If true, in two weeks, they have killed almost 400 civilians, in places way beyond the areas they control in Syria and Iraq. And they would have managed all that while being challenged on the ground by Kurdish fighters and bombed from the air, by coalition war planes, over 8,000 times. Can IS be defeated? We have gone back to the same expert witnesses we met the first time we asked the question. Now, over a year later, we want to know whether their answers have changed.(Photo: Female Kurdish soldier on the frontline against ISIL, Credit: Getty Images)

New research suggests plants might be capable of more than many of us might expect. Some – controversially – even describe plants as “intelligent”, or even “sentient”. So, this week, we’re asking: have we underestimated plants? Our expert witnesses include an academic studying how networks of trees communicate through what she describes as a “wood wide web”, and the pioneer who is using plants to develop robotics.(Photo: US-Fall-Shenandoah, Credit: Getty Images)

Syria’s cultural heritage is being attacked from all sides - the Assad regime, opportunistic looters, opposition forces, Islamic State fighters and even Russian air strikes. Ancient sites like Palmyra have been destroyed, and it is feared that hundreds of precious valuables have been smuggled out of the country to be sold on the international art market. Is it too late to save Syria’s antiquities? We speak to experts including the specialist trying to recover stolen items being sold on the global antiquities market, the volunteer organising a kind of archaeological resistance inside Syria, and the team reconstructing the country’s historic sites using technology. (Photo: Baalshamin detonation, Credit: AP)

Mohammed Akhlaq’s murder shocked India. A mob broke into his house last month and beat him to death. They believed a rumour that Mr Akhlaq, a Muslim, had broken a Hindu taboo by slaughtering a cow. We find out how the cow became such a political animal and look at whether Hindu nationalists are feeling bolder in today’s India. (Photo: An Indian woman sprinkles yoghurt paste onto a cow's forehead. Credit:Getty Images)

Rhinos are in trouble. The ancient Sumatran rhino has just been declared extinct in Malaysia, following the fate of black rhinos in West Africa in 2011. Central Africa's northern white rhino has been reduced to four - yes, four - animals, and conservationists say the more plentiful southern white rhinos are under unprecedented attack from poachers eager to sell the horns to Asian and Arab buyers. This week The Inquiry hears four very different answers to the question: How do you save the rhino? Experts include Namibia’s first female dangerous game professional hunter and one of China’s biggest celebrities and campaigner, Yao Ming.(Image: A baby rhino and an adult rhino. Credit: Getty Images)

Oil accounts for around 75% of Nigeria’s economy, but no-one knows how much the country produces or refines. It means corruption is rife. Hundreds of thousands of barrels of oil are stolen every day, at each level of the supply chain. It is a problem that has cost the Nigerian economy billions of dollars, and weakened its public services and infrastructure. Schools and hospitals are paid for, but never built; citizens are forced to pay bribes for basic services. Many believe Nigeria’s new president, Muhammadu Buhari, is the man to end this decades-old problem. He says he will do it, and has taken personal control of the oil ministry. But it is a huge task he has set himself. So, can Nigeria end oil corruption?(Photo: Buhari inauguration. Credit: AP)

Russia’s intervention in Syria caught the world by surprise. Moscow gave Washington just one hour’s notice before it began its aerial bombardment. Russia claims its jets are attacking the so-called Islamic State. But reports suggest the Russian pilots are in fact targeting groups linked to the Free Syrian Army - the main opposition to Syria’s President Assad, who is a Russian ally. It is the first time President Putin has deployed force beyond the borders of the former USSR and another dramatic step in his increasingly assertive foreign policy. But Josh Earnest, President Obama’s press secretary, has described Russia’s action as motivated by “weakness”. Is he right?Ambassador William Courtney of the Rand Corporation argues that the Middle East is the last place in the world where Russia can play a great power role, and that Syria is the last place in the Middle East where Russia can exert its power. Andrei Kolesnikov explains what he sees as Russia’s weaknesses; a weak economy, declining living standards and a working age population that is deteriorating.Dr Andrei Korolev disagrees. While international isolation and a faltering economy may have forced Russia to adapt, he says, it has done so in ways that make it stronger such as by forming a new alliance with China. The Hudson Institute’s Hannah Thoburn explains how a new politics is emerging. Russians are being asked to accept financial sacrifices in order to help return the country to its place as a global super power, and that so far its working. (Photo: President Putin at the UN General Assembly. Credit: Getty Images)

The CIA has just released 2,500 top secret presidential briefings from the 1960s. The President’s Daily Brief – or PDB – is the US intelligence agencies’ best assessment of global threats, delivered directly to the president every morning. The CIA’s director, John Brennan, has described the PDB as “among the most sensitive and classified documents in all of our government”. The decision to release some PDBs, even documents relating to events many decades ago, was not taken lightly. And, the briefings highlight an almost impossible dilemma – one still faced today by every Director of National Intelligence - what should, and should not, be said? The president cannot absorb everything - there has to be a choice. We explore the relationship between the intelligence, the advisers and the president. What does the president need to know?(Photo: President Lyndon B. Johnson (seated, foreground) working with (background L-R): Marvin Watson, J. Edgar Hoover, Sec. Robert McNamara, Gen. Harold Johnson, Joe Califano, Sec. of the Army Stanley Resor. Credit: LBJ Library)

The United States, UK, Israel and now Pakistan all use drone strikes to kill. In September a general in the Pakistani army announced their first ever use of an armed drone. It was directed at a terrorist compound, he said, and killed three. Meanwhile the US is thought to have launched a secret drone campaign to kill so-called Islamic State fighters in Syria. Armed drones are the counter-terrorism weapon of choice, capable of killing militants from a distance and without putting military personnel in harm’s way. But critics question how far they bolster wider attempts to defeat terrorism. So, do drone strikes work?(Photo: Reaper flies without pilot. Credit: Getty Images)