The West Indian had figures of 21 for one after just four legitimate deliveries, as his first over included a no-ball and three wides, two of which hurtled past the startled wicketkeeper Adrian Aymes for boundaries, each adding six to the score.
McLean regained some pride and poise by yorking Piran Holloway for a duck with his third legal delivery, but then Richard Harden decided to join in the merriment by lashing McLean to the boundary.
After that hectic start the game, almost inevitably, had to settle down, but not before McLean gained some measure of revenge on Harden by dismissing him with a vicious lifting ball that the Somerset batsman could only fend into the hands of the waiting Giles White.
Experience was called for, and Mark Lathwell arrived at the crease to steady things, helping his captain Peter Bowler - who had watched bemused from the other end as the action unfolded - justify his decision to bat.
The calm partnership of 132 that unfolded enabled Bowler to enjoy the best day of a so far frustrating season as his side finished the day on a healthy 245 for 4, with the captain unbeaten on 85.
Timing the ball exquisitely, Lathwell reached a half-century off 84 balls, with seven fours, and had added four more boundaries by the time he fell to a loose shot, caught at square leg off Dimitri Mascarenhas. He was replaced by Keith Parsons, who like Bowler had been short of runs, went on to reach 58 before falling lbw to seamer Kevan James.
At Canterbury, Kent's mixture of youth and experience struggled against Oxford University, with the students enjoying the best of a rain-shortened day after putting their County opponents in to bat.
The Dark Blues' captain Jim Fulton decision was fully justified by his team's performance in the field, a tight, accurate display restricting Kent to 169 for seven from 53 overs in the student's last work-out before next week's Varsity Match at Lord's.
The elements also undid the England fast bowler Darren Gough, who had been hoping for a vigorous work-out after his lay-off with a broken finger. There was no play at Headingley where Yorkshire should have been playing Cambridge University, costing Gough valuable bowling time before next week's third Test at Old Trafford.