‘Why the hell should I believe your lies?’ Nicola Isbitt demanded, the baby in her arms wrestling to get free.

Kate wound her window down so she could hear the ensuing argument better.

‘I’m not lying to you,’ Isbitt pleaded from the rear of his latest company car. His wife, leaning out of the front door of the house, was wearing little more than a dressing gown, and her hair was wrapped up in a towel. Isbitt lifted a small case from the boot of the car and rested it on the paved driveway.

‘I wonder what that’s about,’ Laura muttered. ‘I hate prying, but we should probably ask them to go indoors before one of their neighbours reports it and gets in the way of our enquiry.’ She reached for her door handle.

Kate raised her hand. ‘Hang fire, let’s see where this goes for a bit longer. Okay? If he is our man, let’s find out exactly what his wife thinks of him. If we go in all guns blazing now, she’ll close up, and won’t utter a word against him.’ A noise on the street caught her attention and she turned back. Isbitt had now picked up his case and was striding towards the front door, but his wife, now minus child, was blocking the doorway. ‘Is she holding a phone?’

Laura studied the scene. ‘I can’t quite tell. She’s holding something, oh, and now she’s showing him.’

‘You neglected to mention that she would be there too,’ Nicola howled. ‘How convenient. The same night you’re at a conference in Colchester, she’s at the same bloody conference. Do you really think I’m that stupid?’

Isbitt glanced around for the first time, but missed the car parked across the street where Kate and Laura were straining to hear every word.

‘Where did you get this from?’ he shouted, grabbing the device.

‘It isn’t hard to check other people’s photographs on Facebook you know,’ Nicola fired back. ‘I suppose at least she had the decency not to post a picture of the two of you together.’

‘How many times, Nicki, I am not having an affair with Amelia.’

‘Oh no? So how come the two of you happened to be staying in the same hotel last night?’

He dropped his case and opened his arms passively. ‘I don’t know what you want me to tell you. The conference was at that hotel. I had no idea she would be there. In fact, had you not showed me this photograph, I wouldn’t have even known she was there.’

Nicola folded her arms. ‘Try again, Gavin. At least have the decency to admit you’re screwing her. It wouldn’t hurt as much if you were just honest with me.’

‘Read my lips, Nicki: I AM NOT SCREWING AMELIA. I haven’t seen or spoken to her in more than two years. In fact, I haven’t spoken to her since she left the company. I don’t know where she’s working now, but clearly whatever she’s now doing it must still involve IT. Shocking. I don’t know what else I can tell you. Call her up if you don’t believe me. Ask her if she saw me last night. Ask her when we last spoke.’

‘Oh, you’d like that wouldn’t you? I bet the two of you would have a good laugh about that behind my back!’ Nicola’s eyes widened, and she swung an arm at him.

Kate and Laura were both out of the car without a second’s thought. Laura reached the driveway first, holding her ID aloft. ‘Sir, madam, please take this inside. Now.’

‘That man is not coming into my house,’ Nicola replied, standing firm.

Kate tentatively approached her. ‘Why don’t you and I go inside and discuss things, while my colleague asks your husband a few questions. Is that okay?’

A look of confusion descended. ‘Questions? What about?’

‘I’ll explain when we’re inside,’ Kate urged. ‘Please?’

Nicola watched her carefully, before stepping aside and allowing Kate to enter. She made sure to close and lock the door behind her. Kate followed her through to the dining room where she’d first spoken to Isbitt on Friday. The child she’d been holding at the door earlier couldn’t have been much older than a year and was playing happily in an enclosed pen.

‘He’s cute,’ Kate commented, nodding at the child.

‘Yeah, well hopefully he won’t grow up to be a cheat like his father.’ She apologised when she realised what she’d said.

‘Who’s the woman on the phone?’ Kate asked, keen to expose the gap in Nicola’s emotional barrier.

Nicola slid the phone across the table. Kate was surprised at just how striking the woman in the image was. Tall, with raven-black hair and a figure to die for. ‘She used to work with my husband, until I discovered they’d slept together. I only agreed to take him back if she left the company and he promised not to cheat again. I should have listened to that voice in the back of my head: once a cheat, always a cheat.’

Kate pushed the phone back. ‘Did I hear correctly: they were both at a hotel last night?’

Nicola narrowed her eyes. ‘He was at a conference in Colchester, staying at the Marriott. Ever since the affair, I’ve kept my eye on him. I know I should trust him, but it’s not easy, you know?’

‘I understand, Mrs Isbitt. Between you and me, I think you were brave to take him back in the first place. I know I couldn’t be so forgiving.’

Her shoulders relaxed a little. ‘Please, call me Nicola, or Nicki.’

Kate offered her a reassuring smile. ‘Okay, Nicki. This Amelia woman, how do you know she was also in Colchester?’

‘We have a mutual friend on Facebook. It isn’t hard to keep up with her posts. She doesn’t tend to write much, but she does post the occasional photograph. As she did last night. From the Marriott in Colchester. Some people really should update their privacy settings.’

‘I see, and you think the two of them were meeting up?’

‘What else can I think? It’s only a two-and-a-half-hour drive from Colchester to home, yet he insisted on staying overnight. And I mean, who the hell holds a conference on a Saturday, anyway? I was suspicious from the moment he told me he had to go.’

‘Are you certain your husband was in Colchester last night?’

‘He showed me the email confirming his reservation. Unless he cancelled it at the last minute, he was there.’

‘The reason I ask is…’ She paused for effect. ‘Another woman was murdered and left in the back of a car last night. We have reason to believe she was killed by the same person who stole your husband’s car.’

The blood drained from her face. ‘How do you know it’s the same person?’

‘The victims were killed in a similar way. Now, the reason we’re speaking to your husband is that we have reason to believe that he was in the vicinity at the time of the second murder. When we spoke to you on Friday you advised us that your husband was home all night on Tuesday. In light of this new evidence and what you believe he has been up to, I’m wondering if you wish to revise your statement?’

‘You think Gavin killed those women? My Gavin?’

‘We certainly can’t rule him out at this stage.’

‘He’s not a…’ Her words trailed off.

Kate reached for her hand. ‘Forgive me if I’m speaking out of turn, Nicki, but I can see some faint bruises on your neck and arm… you’re safe here with me and you’re free to speak openly. Has Gavin ever hit you?’

Nicola pulled her hand away and pressed it against the patch of colour on her neck.

Kate leaned closer. ‘You don’t have to be afraid. I have spoken to dozens of women in exactly the same situation as you. You feel trapped because you have a child to take care of. All I’m saying is, you don’t need to be scared. There are people and programmes out there who will protect and help you.’

There was a coldness in Nicola’s eyes as she spoke. ‘I want you to leave my house.’

‘Please, Nicki. My colleague will keep your husband at bay. Okay? He’s not going to get in here, or retaliate. I just need you to be honest with me. Where was he on Tuesday night?’

‘I’ve told you: he was here.’

‘All night?’

‘Yes.’

‘And you’re certain he didn’t get up and leave? If you have any reason to doubt what I’m saying, the man we’re looking for beat and suffocated these women, who can tell what he might do next? Please, Nicki, I don’t want you to be another victim.’

‘He was in bed with me when I went to sleep, and he was there when I woke up.’

‘And he was there all night? Did you wake up at any point in the night and see him still there? Maybe you went to the toilet or got up to check on the baby? I need you to remember.’

Nicola looked nervously towards the front door.

Kate saw the movement. ‘Don’t be afraid. If he’s the man we’re looking for, we’ll take him in now and he won’t ever bother you again. Two women are dead already. Don’t be the reason there’s a third.’

Nicola looked back at her, tears welling in her eyes. ‘I suffer with migraines sometimes. I felt one coming on, on Tuesday night, so I took one of my pills. They knock me right out. All I can tell you is he was there when I went to sleep, and there when I woke up. Whether he was there or went out in between, I – I really can’t tell you.’ The tears broke free and rolled down her cheeks. ‘Oh God, do you really think he…?’

Kate jotted Nicola Isbitt’s comments in her book, found a tissue in a box on the side and passed it to her. ‘He’s now our prime suspect. We’ll monitor his phone and vehicle movements for both dates, as well as checking if his DNA profile is at both scenes. Thank you, Nicki. I promise I’ll keep you safe.’

Kate left the room, unbolted the front door and stepped out into the cool breeze. Laura was leaning against a wall with her arms folded, while Isbitt paced around on the driveway.

‘Finally!’ Isbitt declared. ‘Can I go into my own house now?’

Kate raised her arm to block his path. ‘I’m afraid not.’

He tried to push past, but she grabbed his arm and pulled it behind his back, pressing her knee into the back of his. He dropped to the ground. ‘What the bloody hell are you doing?’

‘Gavin Isbitt, I am arresting you on suspicion of the murders of Helen Jackson and an as-yet-unidentified victim. You do not have to say anything. But, it may harm your defence if you do not mention when questioned something which you later rely on in court. Anything you do say may be given in evidence.’ She cuffed his wrists and helped him to his feet.

‘Murder? What the hell did she say to you? I’m not a murderer. What the hell is going on?’

Kate didn’t respond, leading him to the car and securing him in the back. She took Laura to one side. ‘What did he tell you?’

‘He said he was at some conference in Colchester last night.’

‘That’s what the wife said too. But I’m not convinced.’

‘You think we’ve got our man?’

Kate considered the question. ‘We need to get SSD to check the second vehicle for traces of his DNA. If they find a match, I think we’ll have a better idea. You and Patel had best interview him, but I’d like to observe.’

Laura radioed control to confirm they were bringing him in. Kate knew there’d be no way to keep her involvement from Underhill or the supe. But if she was right, and they’d caught the killer, she wouldn’t need to justify her actions.