Lindsay and Danny always had an interesting relationship that began with teasing and escalated to flirting. Mid season three Lindsay stood Danny up, saying that it was her not him and that she had some things she had to deal with.
After the trial in Montana, they began a relationship that turned intimate in Snow Day. However, the relationship seemed rocky if not ended by the end of season 4, when Danny cheated on her with another woman. It is unknown whether Lindsay was aware of the indiscretions. Eventually though, they slowly started to reconcile when it was revealed that Lindsay was pregant with Danny's child.
Danny and Lindsay are currently married with one child, a daughter named Lucy.
Danny initially expressed resentment towards Lindsay upon her arrival, since Aiden Burn, who Lindsay replaced, was his partner and best friend. When he meets Lindsay at the zoo on her very first case, he tells her to call Mac "Sir," a title which the CSI supervisor takes offense to. Soon after, Danny begins to call Lindsay "Montana," a name that begins disparagingly but quickly turns endearing.
Despite their rocky start, Danny and Lindsay become friends. In "All Access," Lindsay, troubled about Stella's hostage situation, becomes frustrated during an interrogation and walks out of the room. Danny gives chase and talks Lindsay into returning to the interrogation.
Though Danny and Lindsay work a good number of cases together, they manage to see each other on several occasions when they are not working the same case. Lindsay invites Danny to a jazz club in episode 214, "Stuck On You," so they can watch Mac playing bass in his down time. In "Cool Hunter" (episode 216), Lindsay asks for Danny's help with recreating a crime scene by having him carry her through a garden. At the end of episode 215, "Fare Game," Danny sits down with Lindsay to share an insect-based banquet that he had bought on a bet that she wouldn't eat bugs.
In episode 302, "Not What It Looks Like," Danny's true feelings for Lindsay emerge; he protests when she volunteers to go undercover and embraces her after her near-fatal situation is diffused. In the following episode, "Love Run Cold," Danny is shown to have asked Lindsay on a real date but she did not show. When confronted by Danny about their relationship, she tells him that although she "likes him a lot," she cannot be in a relationship with him at the moment. Though disappointed, he still offers his support to her. Lindsay's reason for rebuffing Danny is later revealed to be un-dealt with trauma pertaining to the senseless murder of her friends when she was a teenager.
Because of Lindsay's withdrawal from Danny, their relationship for most of Season 3 is professional and strained. In "The Lying Game," Lindsay leaves for Bozeman to testify for the state against Daniel Kadence, the man accused of murdering her 3 friends and the waitress. Rather than say goodbye to Danny in person, she leaves him a card and signs it "Montana." In "Sleight Out Of Hand," Danny unexpectedly shows up in Bozeman to lend her moral support during the trial. They sit with hands entwined when the verdict is read. Afterwards, Danny hugs Lindsay, and she moves to kiss him, but the moment is interrupted by reporters.
In the third season finale, "Snow Day," Danny and Lindsay awaken on the pool table in Danny's apartment, wrapped in each other's arms. Later on, Lindsay recalls how their evening of drinking and playing pool ended up with them having sex on the pool table.
Although there is little screen time devoted to the personal relationship between Danny and Lindsay during the beginning of the fourth season, they were assumed to be dating. Midway through Season 4, Danny's neighbor's son, Ruben Sandoval, is accidentally killed in the course of a bodega robbery. Blaming himself for Ruben's death, Danny begins to push Lindsay away in grief and begins an affair with Ruben's mother, Rikki. Lindsay confronts him about pushing her away and is hurt when he is withdrawn and aloof. She tells him that she was foolish for allowing herself to fall in love with him so easily and that she will find a way to fall out of love with him. Danny later tries to apologize but they are called away on a case.
In episode 417, "Like Water for Murder," an awkward moment between Lindsay and Danny causes her to leave a piece of evidence unattended. The investigator accrediting the lab notices this, and brings it to Mac's attention. Mac has words with Lindsay, and she verbalizes regret at having entered into a relationship with her coworker. In episode 419, "Personal Foul," Danny calls Lindsay to apologize for pushing her away and he suggests that she come over to his apartment. Although it is not shown, she accepts his offer and apology.
As the fifth season begins, Lindsay and Danny are apparently still in a relationship, though some strain is evident. In episode 509, "The Box," after being caught coming out of a ob-gyn clinic, Lindsay reluctantly admits to Danny that she is pregnant with his child. After struggling with how to deal with the revelation, especially after her remark that she "knows him" and does not expect anything of him, Danny stands by Lindsay and accepts his impending fatherhood. He proposes to her in the following episode, "The Triangle." Lindsay declines, later explaining that she is not refusing outright, but that she merely feels that it is the wrong time. She reminds him of the baby, and suggests taking baby steps. Agreeing, Danny tells Lindsay that he loves her, which she reciprocates. Together, they tell Mac about the pregnancy, and Mac congratulates them.
Subsequent episodes show Danny clearly wanting very much to be a part of the baby's life and Lindsay allowing him to be; on at least two occasions, he interacts with Lindsay's expanding belly. In episode 517, "Green Piece," Lindsay is planning a trip to Montana to see her family before she gives birth. Danny talks to Mac about his relationship with Lindsay and the soon-to-arrive baby. At the end of the episode, Danny takes Lindsay to city hall under the guise of meeting some friends. Outside the city clerk's office, he reiterates his feelings for her and says that he is the man she wants him to be. After Lindsay admits that he is, Danny again asks her to marry him. She agrees, and when the door to the clerk's office opens, she sees Mac and Stella, the friends that Danny was eager for her to meet. Mac and Stella then bear witness to Danny and Lindsay's wedding as a montage of scenes plays, from the couple's first meeting in season 2 episode "Zoo York" up through episode 511, "Forbidden Fruit."
At the end of episode 519, "Communication Breakdown," Lindsay, who is still in Montana, texts Danny that their baby is a girl. By episode 523, "Greater Good," she has returned to the lab and goes into labor in the hallway. Adam takes her to the hospital, where, with Danny at her side, she gives birth to a baby girl. Though they initially disagree on the baby's name (Lindsay wants to name the baby "Lydia," but Danny prefers "Lucy"), they do agree that they want Mac to be the baby's godfather, to which he agrees without hesitation. In the following episode, "Grounds For Deception," Lindsay and Danny have apparently agreed that their daughter's name is Lucy, and have brought her to the lab, where their co-workers, including a male co-worker that a jealous Danny is annoyed that Lucy has responded positively to, coo endlessly over her.
By season 6, a month after the events of the season 5 finale, Danny is shown to be confined to a wheelchair, due to being shot while protecting Lindsay from a drive-by shooter at a bar. Lindsay is shown encouraging Danny to not give up on recovery and assuring him that she'll stay with him no matter what, and even stating that she firmly believes that he will be alright, no matter how high or low the chances of a recovery are. Later on in the episode 603, "Lat 40° 47' N/Long 73° 58' W" Danny tells her that he would work as hard as he could so he could run through the park with his daughter on his shoulders, run down guys who hit on her [Lucy], and that he wanted to dance with her and Lindsay at Lucy's wedding. At the end in episode 604 "Dead Reckoning" Lindsay hears Lucy fussing over the baby monitor so she gets up to soothe her, but instead to her suprise sees Danny standing up on his own two feet holding Lucy in the nursery.
- Unbeknownst to the producers, Anna Belknap was pregnant with her second child at the time "Personal Foul" was being filmed. When she told them of her condition later on, rather than conceal the pregnancy as they had in season 3, they decided to work it into the upcoming season's storyline.