“It’s been challenging but we’ve come through it,” said Reform’s chief whip in the Senedd, Llŷr Powell, as he reflected on the past seven days.

The week began with the party’s leader in Wales being arrested on suspicion of assault and controlling or coercive behaviour.

Dan Thomas said he had been “released without charge” and had “done nothing wrong”.

Confirmation of his arrest was swiftly followed by news of a Reform Senedd member’s defection to Plaid Cymru.

This is the story of how that “challenging” week unfolded.

Last Sunday morning, Thomas was at the BBC’s offices in Cardiff to appear as a guest on the Politics Wales programme.

Later that day, he was arrested before being released on bail.

Journalists got wind of the arrest on Monday evening, which is also when senior Reform figures in Wales began to find out.

A few people at Reform HQ in London, including Nigel Farage, had already been told.

On Tuesday morning, Reform Members of the Senedd (MSs) gathered for their weekly group meeting.

With the “rumour mill going wild” there was “confusion” within the group.

Dan Thomas was not present, and the MSs were not given the full picture, but they were warned that the party faced “a tough few days”.

It was soon announced that Thomas would not take his usual spot in the chamber for First Minister’s Questions and would be replaced by his deputy, Helen Jenner.

At that point Reform said his absence was due to “personal reasons”.

But as time went on it became clear that the story was about to break.

A legal letter sent to media organisations by a Reform barrister would not be enough to block the reporting of Thomas’s arrest.

BBC Wales and others had secured confirmation that Thomas had been arrested and so the party needed to act.

That’s when Thomas sent a WhatsApp message to his party’s MSs explaining the situation. Some of them were in the chamber at the time.

In his media statement Thomas said he was standing down as leader.

He remains a Reform MS for Casnewydd Islwyn.

Then came the next bombshell as it emerged that Reform MS for Pen-y-bont Bro Morgannwg Sarah Cooper-Lesadd was defecting to Plaid Cymru.

Reform only found out about it after BBC Wales asked the party for a response to the story.

Moments earlier she had been sitting on the Reform benches and had been due to speak for the party in the chamber.

Most of Plaid Cymru’s MSs – including some government ministers – were only told about the defection plan at their group meeting earlier in the day.

The defection needed the group’s approval and some Plaid MSs wanted assurances that Cooper-Lesadd fully understood what it meant to be a Plaid Cymru member.

The defection was approved with the necessary two thirds majority. But it wasn’t backed by everyone.

At a hastily arranged news conference in the Senedd, Cooper-Lesadd said her switch to Plaid followed “a period of reflection and deliberation” and that she had found “the right political home”.

The move was completely unconnected to Dan Thomas’s arrest.

Neither Cooper-Lesadd nor Plaid will say how or when the talks over the defection began, only that the process had gone on for “a while” and she had been on a “journey”.

The defection, just four months on from May’s Senedd election, has raised fresh questions about the electoral process where voters were required to back a party rather than an individual.

Jess Blair, from the Electoral Reform Society, said that while defections were “nothing new” there was more of an “accountability gap” given the Welsh voting system.

“When this electoral system was put in place a review mechanism was also built into that process and what we need now is to really see that review take place,” she said.

By Wednesday, Reform’s focus was on appointing a new leader.

A party official from London came to explain the process to MSs, and Dan Thomas was also at that meeting.

As is the case when a new leader is needed, various names were being discussed.

James Evans was seen as one obvious contender.

When it was announced that he would make a media statement reporters scrambled to hear what he had to say.

“Having consulted with my family…I will not be putting my name forward,” he said, despite “a majority” of the party’s MSs backing him to take over.

By Thursday morning it was looking increasingly likely that Helen Jenner would be the next leader.

While Reform UK bosses in London have not had any formal input to the process, sources say there have been “signals” that Jenner – a Farage ally since the UKIP days – would be seen as a good choice in HQ.

Confirmation of Jenner’s appointment is expected as soon as Monday.

“I feel we’re more united than ever,” said Llŷr Powell.

“For us it’s a new start next week and that’s what we’re building on.”

Politics Wales is on BBC1 Wales at 10:00 BST on Sunday 20 September and iPlayer.