Howard married fellow archaeologist Janine Brown shortly after the death of her first husband, Paul, in 1979. (AUDIO: The Reaping) He already had two children of his own from a previous marriage. According to one account, he sexually abused Peri when she was a teenager, cowing her into keeping his actions a secret; Peri indeed stayed silent, though she never forgave him. (PROSE: Shell Shock)
Whilst off the coast of Lanzarote on 9 May 1984, he found an artefact from the planet Trion and briefly met the Fifth Doctor and his companion Vislor Turlough. After the Master remotely took control of Kamelion, he briefly used the android's shapeshifting abilities to take the form of Howard, explaining his presence in the TARDIS control room as having followed Turlough and Peri in; having gotten close enough to the control console to set new coordinates, the Master dropped the disguise. (TV: Planet of Fire)
After Peri left with the Doctor, Howard had the police on the lookout for her, thinking she had just runaway. (PROSE: When It Was Fun) By September, Howard and Janine's marriage had fallen apart, due to Janine blaming Howard of being at least partially responsible for Peri's sudden disappearance from Lanzarote. (AUDIO: The Reaping)
Behind the scenes
The idea, posited in the short story Shell Shock, that Howard abused Peri as a teenager was intended to tie in with an infamous scene in Planet of Fire in which Peri, having a nightmare and taking in her sleep, cries out Howard's name and begs him "please don't turn out the light". It, however, conflicts with that same scene, since Peri also begs him not to leave her on her own, the very opposite of the plea one would give in such a situation. Indeed, it was contrary to the intents of the actors and director, as relayed on the DVD commentary for the story. Although never explicitly contradicted in any official narrative media, the idea went unmentioned by The Reaping and Peri and the Piscon Paradox, both of which revealed much about Peri's early family life, including her history of abuse and Howard and Janine's divorce, both situations where one might expect such a thing to come up. Furthermore Have You Seen...? and When It Was Fun both portray Howard as genuinely concerned about her when she disappeared, not what you'd expect from an abuser. Shell Shock therefore stands as an oddity in Howard's in-universe biography not really backed up by much else.