St Thomas a Becket church in Somerset is on the heritage critical list and badly in need of rescue. A flood in 1968 led to the church's eventual deconsecration and it is just one of many churches in Britain that has been declared redundant. Decline in church-going and amalgamation of parishes have put a huge swathe of our architectural heritage in peril. Working their way up the property ladder, newly-weds Paul and Laura spotted the church in 2007 and decided this was the family home for them. They purchased the listed church with plans to turn it into a three-bedroom home. As the church is transformed, its past emerges - the dark times which marked its end and its links to an architectural movement that would change style forever, connecting it to the design of some of the greatest buildings in the country.

Nutbourne pumping station in West Sussex is a wreck. It closed in the 1970s and is now an industrial-size bunker full of rusting, redundant, heavy duty machinery. But this ruin was at the heart of a revolution that saved our grandparents' generation and changed society forever. Its remarkable past doesn't stop there, it was slap bang in the heyday of architectural design and played a crucial role in the dark, dismal years of the 1930s depression. For new owners Nick and Brigitte, the rotting bunker offered the ideal space for them and their five-year-old twins. Their plan is ambitious - turn the concrete carcass into a carbon efficient home for life. When the couple first bought the pumping station, they had no sentimental attachment to its former life. But as they learn about its past, their feelings towards the building begin to change.

Stoke Hall is a 30-room Georgian mansion whose future has been far from certain for decades. The leaking roof and widespread rot makes securing the building difficult and expensive. At risk of being lost forever is the Hall's 250-year-old Georgian décor which miraculously has survived. Local, childhood sweethearts, Steve and Natalie, started married life in a 3-bed semi. Now he is a self-made millionaire with a successful business supplying high-tech products to the energy business. As the restoration starts, the past life of the house begins to emerge revealing architectural and social connections to the highest and most influential people in the land.

Years of neglect have left fungus growing on walls running wet with damp and timbers so rotten that one good storm might bring down the roof. Stanwick Hall is in appalling condition and faces an incredible battle for survival, which City high-flyers Gina and Simon have taken on. The Hall is on the buildings-at-risk register which means it is one of the most endangered structures in the country. As the restoration throws up more and more serious problems, long forgotten evidence comes to light showing it was built on the biggest financial scandal of the early 18th century and was emblematic of the huge upheaval in the early 19th century that changed the landscape of Britain forever.

Calverton Manor is a collage of different architectural styles with parts thought to date back as far as the 14th century. And it comes with its very own legend involving a rich widow, the local butcher, pots of gold and murder. As the building's architectural and historical secrets begin to emerge - including high treason and arranged marriages - owners David and Jeanette are faced with a renovation that is causing problems. A main beam holding up the house has been destroyed by woodworm - it's a miracle the building hasn't collapsed. Whilst the building's past secrets are a constant fascination for the history-loving owners, the restoration process is proving to be much more testing than anyone predicted.

Once a building of grandeur and influence, Big House is now a carcass. But digging deep into the archives, the property's historical and architectural roots, gives an insight into the wealth and power of an empire built on one of the country's most precious commodities - coal. And it provides an intriguing tale about the dirty tricks of political corruption. Why did this house fall into rack and ruin? Can it ever be returned to its former glory and who can tell what it looked like in its heyday? Owner, Alun, has lived in this part of the world all his life and dreamed of owning Big House ever since he was a small boy. Almost 10 years ago, he bought it. He's got a big job on his hands. Progress has been painfully slow but his aim it to turn Big House into a home.