After 15 years of comparatively trouble-free operations, high-speed train company Eurostar is now facing huge challenges.
The company's bosses must get to the bottom of a cold weather malfunction of trains that appears baffling - even to rail experts.
And they must then win back the trust of the travelling public -a trust which will have been eroded by all the tales of travel misery that emerged this weekend after the train failures within the Channel Tunnel.
If it was a simple mechanical failure of a piece of equipment, then things would be relatively simple for Eurostar.
But what the company has said is that its problem with the trains this weekend has been to do with the changes between the sub-zero temperatures outside the tunnel and the 25C (77F) heat within the tunnel.
Yet Eurostar has been running since 1994. There have been numerous cold snaps in that time, with the trains running from London through Kent - one of the UK's snowiest counties.
What the company has to work out is just why this problem has arisen now and not in the past.
"It's all a bit of a mystery and the company, and indeed a lot of people, appear baffled by it," said Nigel Harris, managing editor of Rail magazine.
He went on: "The fact that the problem has affected London-bound trains rather than ones leaving St Pancras may have been due to the fact that those heading away from London have less time to get cold.
"They pass through miles of tunnel through London and then go under the Thames and they just don't have time to get exposed to the very cold temperatures before going into the tunnel."
Mr Harris continued: "But what is really puzzling about this is the fact that it is happening now, even though the trains have been exposed to cold weather over the last few years.
"The Eurostar trains are effectively TGVs (the French high-speed service) and they've been going even longer than Eurostar without experiencing any of these cold-weather problems.
"Eurostar must try to sort this out as soon as possible as any further problems will do them huge reputational damage. They have promoted themselves as the 'green', stress-free alternative to flying and now they face a major technical issue that they need to get on top of."
Eurostar has suffered two serious in-tunnel fires during its 15-years of operation. But despite those setbacks it has become the way to travel between London and Paris and Brussels.
Already popular, the service was given a further boost when the 68-mile London to Folkestone Channel Tunnel high-speed rail link - now known as HS1 - was completed in 2007.
This enabled passengers to travel to Paris from London in two hours 15 minutes, while London-Brussels journey times came down to one hour 51 minutes.